Interview Questions and Answers for freshers and experienced pdf Mechanical Engineering

1. Define primary and secondary transducers ?
Ans:  A primary transducer senses a physical phenomena and converts it to an analogous output.
The analogous output is then converted into an electrical signal by secondary transducer.

 2. How many links and turning pairs are required (minimum) for a kinematic chain ? How many will be instantaneous centres for such a chain ?Ans:  4 links and 4 turning pairs. Six instantaneous centres.

 3. When does a kinematic chain become a kinematic mechanism ?Ans:  When any one link is fixed.

 4. When Coriolis component is encountered ?Ans:  When a point moves along a path that has rotational motion.


 5. Where the pitch point on a cam located ?
Ans:  It is the point on cam pitch curve having the maximum pressure angle.

 6. What is the basic circle of a cam profile ?
Ans:  It is the minimum radius circle drawn to the cam profile.

 7. If the ratio of tight side to slack side tension on belt drive is increaseed by %, how much power transmission will increase ?Ans:  By %.

8. What is the effect of creep of belt in belt drive ?
Ans:  It decreases speed of driven pully and the power output.

9. What is the difference between kinetics and kinematics ?
Ans:  While kinematics studies the motion of a body without regard to the mass of body and forces acting on it, kinetics does not consider mass or forces.

10. What is the difference between couple and angular momentum and how they are related ?
Ans:  Couple is product of moment of inertia and angular acceleration. Angular momentum is the product of moment of inertia and angular speed. Time rate of change of angular momentum of body is equal to external couple acting on the body.

 11. What is the difference between simple and compound machine ?
Ans:  In simple machine there is one point each for effort and load but in compound machine there are more than one point for application of load and effort.

 12. What is the difference between mechanical advantage and velocity ratio ?
Ans:  Mechanical advantage is the ratio of load lifted and the effort applied. Velocity ratio is the ratio between the distance moved by the effort applied and the distance moved by the load lifted.

 13. Explain the difference between clastic collision and inelastic collision ?
Ans:  In elastic collision, the total momentum and total kinetic energy remains constant before and afater the collision. In inelastic collision the total momentum remains constant but the total kinetic energy remains same before and afte the collision.

 14. What type of gears will you recommend for non-parallel intersecting shafts and non-parallel non-intersecting shafts ?
Ans:  Bevel gears, and cross-helical gears respectively.

 15. In a vibrating system with single degree of freedom how undamped frequency is related to natural frequency ?Ans:  Former is greater.

 16. Differentiate between elastic collision, inelastic collision, and completely inelastic collision.
Ans:  In elastic collision both total momentum and kinetic energy is conserved in collision but in inelastic collision the total momentum is conserved and K.E. is not. In completely inelastic collision the two colliding bodies stick together.

 17. Give example of rigid link and flexible link ?
Ans:  Connecting rod and belt respectively.

 18. What is the difference between higher pair and lower pair ?
Ans:  Higher pair has point or line contact between two links and lower pair has surface contact between two links while in motion.

 19. Which mechanism gives approximate straight line motion and which one accurate straight line motion ?
Ans:  Watt, Scott-Russel respectively.

 20. What are seismic instruments ?
Ans:  Seismic instruments are absolute motion measurement devices to indicate or record absolute displacement, velocity and acceleration of a vibrating body.

 21. Which type of cam would you recommend for obtaining constant acceleration ?
Ans:  Parabola cam.

 22. A fixed gear having  teeth meshes with another gear having 20 teeth form¬ing epicyclic gear train. Centre lines of both gears are joined by an arm. How many rotations small gear will make for one rotation of arm ?Ans:  /20 + 1 = 16.

 23. Whether Whitworth quick return mechanism is an inversion of double slider crank mechanism ?
Ans:  No.

 24. Whether the sensitivity of isochronous governor is zero or infinity ?
Ans:  Zero.

 25. On what factors depends the critical damping ?
Ans:  It depends on mass and stiffness.

 26. For what purpose the bifiler suspension system used ?
Ans:  It is used to determine moment of inertia.

 27. How forced vibrations are dependent on natural frequency ?
Ans:  They are independent.

 28. Out of involute and cycloidal profile, which has constant pressure angle throughout gear tooth contact and which requires exact centre distance ?Ans:  In involute profile, pressure angle is same throughout enagement and cycloidal profile requires exact centre distance between two gears.

 29. On which parameters depends the value of gyroscopic couple ?
Ans:  It depends upon M.I. of rotor, spinning speed, and angular speed of precession.

 30. What is the difference between swaying couple and hammer blow ?
Ans:  Swaying couple is produced due to unbalanced parts of the primary disturbing forces act¬ing at a distance between the line of stroke of the cylinders. Hammer blow is the maximum value of the unbalanced vertical force of the balance weights.

 31. For a flat pivot what is the ratio of frictional moment for uniform pressure vs uniform rate of wear ?
Ans:  4 : 3.

 32. Explain difference between simple mechanism and compound mechanism.
Ans:  Simple mechanism has upto four links and compound mechanism has more than four
links.

 33. What is the difference between plane and spatial mechanism ?
Ans:  In plane mechanism all the links lie in the same plane whereas in spatial mechanism links lie in different planes.

 34. How many degrees of freedom are there in a constrained mechanism ?
Ans:  One.

 35. What is Klein's construction ?
Ans:  It is a graphical procedure of drawing acceleration diagram for a slider crank mechanism.

 36. What type of mechanism is constituted by Peaucellier, Hart and Scott-Russel mechanism ?
Ans:  Straight line mechanism.

 37. What is the difference between fast pulley and loose pulley ?
Ans:  Fast pulley transmits power and loose pulley does not.

 38. What is the value of damping factor for a critically damped system ?
Ans:  Unity.

 39. What are the values of amplitude of vibration at node and antinode ?
Ans:  Zero and maximum.

 40. What is the value of damping ratio for under-damped system ?
Ans:  Less than unity.

 41. On what factors the critical speed of a rotating shaft depends ?
Ans:  Mass and stiffness.

 42. What is the damping ratio for non-oscillating system and under-damped system ?
Ans:  More than unity and less than unity respectively.

 43. What is fundamental frequency ?
Ans:  It is the minimum frequency in the system.

 44. Give three active and passive transducers ?
 Ans:     Active transducers                            Passive transducers
1.    Thermocouples and Thermopiles           Resistive transducers
2.    Moving coil generators                          Inductive transducers
3.    Photovoltaic cells                                  Capacitive transducers

 46. Which is best suited bearing for combined thrust and radial loads at high speeds ?
Ans:  Deep groove ball bearings.

 47. Which parameter determines the life expectancy of ball/roller bearing ?
Ans:  Basic dynamic loading.

 48. Which bearing is suitable for combined radial and axial loads ?
Ans:  Taper roller bearing.

 49. Explain the difference between hydrostatic and hydrodynamic bearings ?
Ans:  In hydrostatic bearings, lubricant is supplied at high pressure to lift the shaft. In hydro-dynamic bearings the hydrodynamic pressure is generated due to rotation of the journal.

 50. What is the ratio of frictional torque produced for uniform wear to frictional torque produced for uniform pressure ?Ans:  3/4.

 51. On what factor the maximum efficiency of screw jack depends ?
Ans:  Angle of friction.

 52. To be on safe side which assumption is advisable for working out (i) power lost in friction ? and (ii) power transmitted by friction ?Ans:  Uniform pressure, uniform wear respectively.

 53. State the conditions for a rigid rotor to be dynamically balanced.
Ans:  When rotor is rotated at high speed, the vibrations in two planes should be within pre¬scribed limits. Rotor should not be operated near its natural frequency of vibrations.

 54. Why involute profile is preferred to cycloidal for gears ?
Ans:  The rack for generating involulte profile on gears has straight line profile and hence such gears can be easily cut.

 55. What is the condition for correct gearing ?
Ans:  According to condition of correct gearing, the common normal to the pitch surface should cut the line joining the centres at a fixed point.

 56. What is the diameter of rack for gear ?
Ans:  Infinite.

 57. Define transducer ?
Ans:  Transducer is an element which converts the signal from one physical form to another without changing the information content of the signal.

 58. What are Herringbone gears and what for these are used ?
Ans:  Herringbone gears are double helical gears and used to eliminate axial thrust.

 59. Whether normal pressure angle in helical gear is more or less than ordinary pressure angle ?
Ans:  Less.

 60. Whether tooth error is more prominent for spur or helical gears ?
Ans:  Spur gears.

 61. Show the variation of the ratio of damped frequency to undamped frequency against damping ratio in case of a damped oscillator ?Ans:  As damping ratio increases, the ratio of damped to undamped frequency decreases nearly exponentially.

 62. A simple gear train has three gear wheels of 25,  and 50 teeth respectively. The speed ratio of third gear to first gear and direction are ... ?Ans:  Half and same direction.

 63. The axes of first and last gear in a reverted gear train are ... ?
Ans:  Coaxial.

 64. Which gear train is used to connect hour hand in clock mechanism to minute hand?
Ans:  Reverted gear train.

 65. If there are even number of idlers between driver and driven gears in a simple gear train, then direction of driver and driven gears will be ... ?Ans:  Opposite.

 66. What for pycnometer is used ?
Ans:  Pycnometer is used to measure specific gravity of the liquid.

 67. How helical gears are capable of transmitting heavy load at high speed compared to spur gears ?
Ans:  Helical gears have smooth engagement and two pairs of teeth are always in contact.

 68. Which type of bearing is most suitable for helical gears ?
Ans:  Deep groove ball bearing.

 69. What is the name given to bevel gears used for connecting non-intersecting shafts ?
Ans:  Hypoid gears.

 70. Out of spur, bevel, helical, mitre, herringbone, hypoid, zerol gears, in which case the interchangeability is possible ?Ans:  Spur gears.

 71. Why worm gear drive is used for hoists ?
Ans:  Because it is self locking.

 72. What is the material used for worm gear pair ?
Ans:  Bronze.

 73. In which type of gear pair heat dissipation is important criterion ?
Ans:  Worm gear.

 74. A gear train in which axes of gears have motion is called ... ?
Ans:  Epicyclic gear train.

 75. If a rigid body is to be replaced by two concentrated masses rigidly connected together then what are the essential conditions for two systems to be kinetically equivalent ?Ans:  (i)   Mass of two masses should be same as the mass of rigid body.
     (ii)  Centre of gravity of two mass system should coincide with the centre of gravity of rigid body.
     (iii) Mass moment of inertia of the two mass system and the rigid body about centre of gravity should be equal.

 76. State D' Alembert's principle and write down its importance.
Ans:  D' Alembert's principle enables us to replace a given system by a massless rigid body so that forces acting on it are equivalent to those on real body and then enables to determine the forces transmitted to other paired rigid body. This way the problem of kinetics gets reduced to equivalent problem on statics.

 77. What is the effect of inertia of reciprocating parts on the engine frame ?
Ans:  Inertia of reciprocating parts subjects engine frame to the force required to accelerate the reciprocating mass and thus subject them to primary disturbing force and secondary disturbing force. Secondary disturbing force comes into play due to obliquity of connecting rod and has twice the fre¬quency of the primary force.

 78. How the reciprocating masses of engine are balanced ?
Ans:  Four conditions need to be ensured for balancing reciprocating masses.
(i)   Primary forces must balance   
(ii)  Primary couples must balance
(iii) Secondary forces must balance   
(iv)  Secondary couples must balance.

 79. Why only partial primary balance is achieved and not full primary balance in case of reciprocating masses ?Ans:  Balancing mass of same amount as reciprocating mass may balance primary force but introduce another unabalanced vertical force. Thus compromise is effected by balancing only a portion of primary forces.

 80. What is hammer blow in locomotives ?
Ans:  Vertical unbalanced force introduced due to balancing weight for balancing primary force at high speeds may be sufficient enough to lift the wheels from the rails and this condition is known as hammer blow.

 81. How may types of bonded strain gauges used ?
Ans:  (a) Fine wire strain gauge   
     (b) Metal foil strain gauge   
     (c) Piezo resistive gauge.

 82. In a spring mass system, mass is doubled and spring stiffness halved. The natural frequency of longitudinal vibration will be ... ?Ans:  Halved.

 83. What is PID controller ?
Ans:  A suitable combination of three basic modes — proportional integral and derivative (PID) used to improve all aspects of system performance is called PID controller. The characteristics of three modes of control are :
Proportional controller    —    Stabilises gain but produces a steady state error.
Integral controller           —    Eliminates steady state error
Derivative controller       —    Reduces rate of change of error

 84. In forced vibrations, how the spring force, damping force and inertia force behave in relation to direction of displacement ?Ans:  Spring force is always opposite to displacement, damping force lags by 90°, and inertia force is in phase with displacement.

 85. On what factors depends the critical damping coefficient ?
Ans:  Critical damping coefficient depends on mass and natural frequency.

 86. Name various functional elements of an instrumental system ?
Ans:  (1) Primary sensing element   
(2) Variable conversion (or) transducer element
(3) Variable manipulation element       
(4) Data transmission element
(5) Data processing element   
(6) Data presentation element
(7) Data storage and playback element.

 87. What is the use of a hot-wire anemometer?
Ans:  It is used to measure the flow rate and used in study of varying flow conditions.

88. Differential between main function of flywheel and governor.
Ans:  The function of flywheel is to reduce fluctuation of speed during a cycle and the function of governor is to control the mean speed over a period for output load variations. Flywheel has no influence on mean speed of prime mover and governor has no influence over cyclic speed fluctuation.

 89. On what factor depends the natural frequency of a system ?
Ans:  It depends on the mass and stiffness of system.

 90. State the condition for the stability of a governor. Whey is an isochronous governor not stable ?
Ans:  For a governor to be stable, the ratio of controlling force and radius of governor balls (r) must increase with increase in radius. Further controlling force must be zero for a certain value of r and be negative below it.
In isochronous governor, ratio of controlling force and radius of governor is constant for all values of radius and as such it is not able to attain a definite position for particular speed.

 91. State Grashof s law for fourbar linkage mechanism.
Ans:  According to it, the sum of the shortest and longest link length can't be greater than the sum of the remaining two link lengths, if there is a continuous relative motion between two members.

 92. State the conditions for a four-bar linkage to be called a Grashof s linkage and also when this linkage would become a double crank mechanism ?Ans:  For Grashof s linkage, shortest link is fixed and sum of shortest and longest link is less than the sum of other two links.
For double crank mechanism, two alternate links are of same length and one of larger link is fixed.

 93. What are inversions ?
Ans:  Inversions are different mechanisms obtained by fixing different links in a knematic chain but keeping relative motions of links unchanged with respect to one another.

 94. How many inversions are possible in a kinematic chain having N links.
Ans:  N inversions.

 95. Name the three stages of a generalised measuring system.
Ans:  (i)   Sensing and converting the input to a convenient and practicable form.
     (ii)  Processing/manipulating the measured variable.
     (iii) Presenting the processed measured variable in quantitative form.

 96. What is the function of an intermediate modifying system ?
Ans:  Various functions of an intermediate modifying system are
(1) Amplification   
(2) Modification (modulation)
(3) Data Processing    
(4) Data transmission.

 97. What is static pressure ? How is it measured.
Ans:  The pressure caused on the walls of a pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to walls of the pipe is called static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid so that the tube is at right angle to the fluid flow path.

 98. State when the meshing surfaces can be called conjugate ?
Ans:  Meshing surfaces are called conjugate when they follow the law of gearing, i.e. the common normal at the point of contact always passes through a pitch point on the line joining the centres of rotation.

 99. Give Kelin's construction and its use.
Ans:  Triangle representing line joining piston centre and crank rotation point, crank and connecting rod is drawn. Connecting rod line is produced to intersect a perpendicular through crank rotation point on line joining piston centre and crank rotation point. Draw a circle with radius equal to projected length and centre as common point on connecting rod and crank. Another circle is drawn with piston centre as centre and radius of length of connecting rod. Draw a line joining points cutting two circles and meeting connecting rod at same point. Polygon joining lines of crank, part of connecting rod, line along chord to central axis and line from last point to crank rotation centre is acceleration polygon.

100. When a tensile member fail in shear ?
Ans:  If its shear stength is less than half of its tensile strength.

Interview Questions for Mechanical Engineering Set7

1. What parameters influence the tool life ?
1. Tool material
2. Work material
3. Speed, feed and depth of cut
4. Tool geometry work system  
5. Cutting fluid  
6. Built up edge   
7. Vibration behaviour of the machine tool.

2. Mention the function of intermediate stage in a generalised measurement system.
(i)   Amplify signal without affecting its waveform
(ii)  Remove unwanted noise signals that tend to obscure the input
(iii) Capable of doing other conditioning like differentiation/integration, A/D conversion etc.

3. What is a signal flow graph ?
 A signal flow graph of a system is a graphical model in which nodes represent the system variables and directed branches between the nodes represent relationship between the variables. In a signal flow graph, a forward path originates from the input mode and terminates at output mode without encountering any mode more than once.

4. Explain the difference between rotational and irrotational flow.
 In rotational flow the vorticity is non zero and in irrotational flow it is zero. In irrota¬tional flow the net rotation of a fluid element about its own mass centre is zero as it moves from one
place to another. For it, dv/dx = du/dy.

5. Define the term stability of a feed back control system ?
 A system is said to be stable if the output of a system after fluctuations, variations or oscilla-tions, settles at a reasonable value for any change in input.

6. What is meant by precision ?
 Precision is defined as the ability of instrument to reproduce a certain set of readings within a given accuracy.

7. What is boundary layer ?
 Boundary layer is the fluid layer in the neighbourhood of a solid boundary where the effects of fluid friction are predominant.

8. On what account the boundry layer exists ?
 Boundary layer m fluid flow exists on account of fluid density.

9. Explain the difference between laminar flow and turbulent flow.
 In laminar flow the fluid particles move along smooth, regular paths which can be pre¬dicted in well advance. Turbulent flow is characterised by random and erratic movements of fluid particles resulting in formation of eddies. For flow to be laminar in a pipe, the Reynold's number is less than 2000 and for flow to be turbulent it is greater than 4000.

10. What is the difference between path line and stream line ?
 A path line is a curve traced by a single fluid particle during its motion. A stream line is an imaginary line drawn in a flow field such that a tangent drawn at any point on this line represents the direction of the velocity vector. There is no flow across the stream line.   

11. What is the difference between steady and unsteady flow ?
 In steady flow the velocity at a given point does not change with time whereas in unsteady flow it changes with time.

12. What is stagnation point and stagnation pressure ?
 A stagnation point is one at which velocity is zero. Stagnation pressure is the sum of static pressure and dynamic pressure.

13. What is the hydraulic-grade line ?
 It is the line which shows tne variation of piezometric head.

14. Under what condition the thickness of thermal boundary layer and hydrody-namic boundary layer is same ? When Prandtl number is equal to unity.

15. What keeps the shaft in floating condition in hydrodynamic journal bearing ?
 Hydrodynamic pressure developed in the lubricant.

16. Why the elements of higher pairs must be force closed ?
 This is necessary to provide completely constrained motion.

17. What is the value of coefficient of friction for ball bearing ?
Ans:  0.1 to 0.25.

18. Why belts are subject to creep ?
 Due to uneven extension and contraction of belt.

19. What is the ratio of damping coefficient to critical damping coefficient called ?
 Damping factor.

20. In which type of lubrication the starting friction is low ?
 In hydrostatic lubrication.

21. Whether Bernoulli's equation is applicable for streamline straight and rotational flows ?
 Ans: Yes.

22. When a plate slides over a parallel plate, what is the relationship between vis¬cous force and the lubricant thickness ? They are directly proportional.

23. How the stability of empty ship increased.
 By adding ballasts at the bottom level.

24. Define Froude number.
 It is the square root of ratio of inertia force to gravity force.

25. What for Maning's formula used ?
 It is used to determine velocity of flow in pipe.

26. What is the maximum efficiency of power transmission through a pipe ?
 Ans: 66.67%.

27. What is the necessary and sufficient condition for bodies in floatation to be in stable equilibrium ?
 Centre of gravity of body should be located below metacentre.

28. Under what condition the thermal boundary layer thickness will be equal to the hydrodynamic boundary layer thickness ? When Prandtl number is unity.

29. How laminar boundary layer thickness varies on a flat plate ?
 It is proportional to the square root of the distance from the leading edge.

30. Name the axial flow reaction turbine with adjustable vanes.
 Kaplan turbine.

31. Define the degree of reaction of a turbomachine.
 It is the ratio of total pressure change in the rotor to that in the stage.

32. What is meant by relative stability ?
 If the system is found to be stable, then it is necessary to know the stable strength or degree of stability which is called relative stability. Phase margin and gain margins are the measures of relative stability.

33. On what factors the efficiency of a centrifugal pump depends ?
 The efficiency of a centrifugal pump depends on size, speed and type number.

34. Define transducer ?
 Transducer is an element which converts the signal from one physical form to another without changing the information content of the signal.

35. A 200 mm impeller of centrifugal pump develops discharge head of 2 kg/cm2. If discharge head is required as 8 kg/cm2, what should be diameter of impeller. Ans: 400 mm.

36. Why thin-plate orifice is frequently recommended for flow measurement in most of the cases ?
 It is recommended because of its high accuracy, low cost, and extreme flexibility.

37. How the water flow from a hydrant in a city water system measured ?
 It can be measured by allowing the flow of water from a hydrant and noting down the horizontal distance (x) where jet strikes the ground and the vertical distance (y) of outlet from ground.
Then flow = area of hydrant x

38. For the same size, length and condition of pipe, how the friction head loss changes if pipe size is varied.
 Under same flow conditions the friction head loss increases as the size change to the 4.8th power.

39. How does the capacity changes in pipe flow with increase in pipe diameter if head is constant ?
 At constant head, capacity is proportional to d25.    .

40. How does the head change in pipe flow with change in diameter, if capacity is constant.
 At constant capacity, head is proportional to

41. How head varies in pipe flow with change in flow, if pipe diameter is same.
 At constant diameter, head is proportional to (flow)2.

42. Give some properties of errors ?
      (i)   Errors give the difference between the measured-value and the true value
     (ii)  Accuracy of a measurement system is measured in terms of error
     (iii) A study of error helps in finding the reliability of the results.

43. Define the term contraction coefficient.
 The ratio of area of jet (contracted) and the cross section of the orifice.

44. What for pycnometer is used ?
 Pycnometer is used to measure specific gravity of the liquid.

45. How may types of bonded strain gauges used ?
     (a) Fine wire strain gauge   
     (b) Metal foil strain gauge   
     (c) Piezo resistive gauge.

46. Name various functional elements of an instrumental system ?
 (1) Primary sensing element   
 (2) Variable conversion (or) transducer element
 (3) Variable manipulation element       
 (4) Data transmission element
 (5) Data processing element   
 (6) Data presentation element
 (7) Data storage and playback element.

47. Name the three stages of a generalised measuring system.
 (i)   Sensing and converting the input to a convenient and practicable form.
 (ii)  Processing/manipulating the measured variable.
 (iii) Presenting the processed measured variable in quantitative form.

48. How is a Pelton turbine braked ?
 A pelton wheel is braked by a nozzle directing a jet on the back of the buckets.

49. What is static pressure ? How is it measured.
 The pressure caused on the walls of a pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to walls of the pipe is called static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid so that the tube is at right angle to the fluid flow path.

50. What are the requirements of a control system ?
 Stability, accuracy and speed of response are the three requirements of control system.

51. What is the difference between weir, and submerged weir.
 Any obstruction of a streamflow over which water flows is weir. When the downstream water level rises over the weir crest, it is called submerged weir.

52. What is the difference between spillway and siphon spillway ?
 Spillway is an essential part of a large dam and provides an efficient and safe means of releasing flood water that exceeds the design capacity of the reservoir.
Siphon spillway is spillway designed to discharge water in a closed conduit under negative pressure.

53. What is the difference between culverts, stilling basin, and standpipe ?
 Culverts are built at the points of lowest valley to pass water across the embankments of highways or railroads.
Stilling basin is transitional energy dissipating structure to avoid the damaging process by a highly accelerated spilled water.
Standpipe is used principally for alleviating the transient pressures in large pipeline system. It also works as a pressure relief valve for the upstream pipe during the turbine shut off.

54. What do you understand by run-of-river scheme in hydro power generation ?
 A scheme in which the discharge is varying and only that much water can be utilised for conversion as available in the river.

55. What is the difference between firm power and secondary power in hydro power plants ?
 The approximate constant and continuous power which is assured at power station and would be available throughout the year is called firm power.
In run-of-the river schemes which are generally designed for % availability of water, the firm power would be available for at least % of the years during the life of the scheme. However in some years discharge in the river may be more than % availability discharge and some extra power known as secondary power can be generated.

56. What is the criterion for determining economic diameter of power tunnel ?
 The economic diameter of a power tunnel is determined such that the total value of following two factors is least
(i) annual loss of revenue on account of power head lost due to friction.
(ii) recurring annual expenditure.

57. What are the three functions served by a surge tank in a hydro plant ?
 The three functions served by a surge tank are
(i)   flow regulation - act as a reservoir for acceptance or delivery of water to meet requirements of load changes.
(ii)  water-hammer relief or pressure regulation.
(iii) improvement in speed regulation.

58. What is the criterion to determine the economic diameter of penstock ?
 The economic diameter of a penstock required to carry a discharge is the one at which annual costs due to the greater investment do not exceed the annual value of resulting increment energy output.

5. If jet ratio for a pelton wheel is 12 then number of buckets should be .... ?
 0.5 x 12+ 15 = 21.

60. What is the difference between anti-friction and hydrostatic bearings ?
 In anti-friction bearings rolling components are introduced between the sliding surfaces. In hydrostatic bearings lubricant is supplied at a high pressure to a pocket in the bearing.

61. What is inviscid fluid ?
 It is the frictionless fluid.

62. State law of conservation of momentum ?
 The ratio of change of momentum of a mass of fluid is equal to the vector sum of all external forces acting on it.

63. Define turbulent flow ?
 Flow in which adjacent layers mix continuously, so that the flow pattern is unsteady, full of eddies, and apparently without any mathematically expressible regularity.

64. Define Reynold's law of similitude ?
 Two geometrically similar flow systems subject only to friction and inertia forces are dy¬namically similar if both have the same 'Reynolds' number.

65. What is the difference between boundary lubrication and fluid film lubrication ?
 In boundary lubrication condition the ratio of thickness of lubrication film to surface roughness (CLA value) is less than 1 and for fluid film lubrication condition this ratio is greater than 5 and less than 100.

66. A bearing in which hydrodynamic pressure is generated due to rotation of jour¬nal is called... ?
 Journal bearing.

67. For a journal running in a bearing clockwise at steady state, where will be the minimum clearance ?
 To the left of the load line.

68. Out of impulse and reaction type hydraulic turbines, which has higher specific speed ?
 Reaction turbine.

69. What is order of the system.
 The order of the system is the order of the highest derivative of the ordinary differential equation with constant coefficients which defines the system mathematically.

70. What is Bode plot ?
 Bode plot is a logarithmic plot used to represent transfer functions. The Bode plot consists of two plots namely.
(i) The plot of magnitude in db (on linear scale) vs. frequency to (on log scale)
(ii) The plot of phase angle in degrees (on linear scale) vs. frequency co (on log scale)

71. Navier stokes equation represents the conservation of which quantity ?
 Momentum.

72. What are the characteristics of precision ?
 (i) If a number of measurements are made on same true value, the degree of closeness of these measurements gives precision
(ii) It is a measure of the degree of repeatability or reproducibility of the measuring system.

73. What is meant by loading ?
 During the act of measurement the measuring instrument takes energy from the signal source or measured medium and thus the signal source is altered. This effect is called loading.

74. Give two uses of Bode plots.
(i) They are the logarithmic plots used to represent transfer functions
(ii) They are used in the calculation of gain margin and phase margin.

75. What is the name of nondimensional group for ratio of inertia force to gravity force.
 Froude number.

76. The head loss in a fully developed laminar flow in a circular pipe due to friction is directly proportional to ... ?
 Square of mean velocity.

77. For what type of flow, the streamlines, pathlines and streaklines are virtually identical ?
 Steady flow.

78. How the streamlines and equipotential lines are related in a flow field ?
 They are orthogoial everywhere in the flow field.

79. Under what kind and condition of a fluid the velocity potential exists ?
 Irrotational flow.

80. Where should centre of gravity of a body lie for it to float in stable equilibrium ?
 e.g. should be located below the metacentre.

81. For fully developed flow through a pipe, what is the ratio of maximum to average velocity ?
 Ans:  2.

82. Out of centrifugal, axial and positive displacement pumps, which has maximum specific speed and which has minimum ?
 Axial pump has maximum specific speed and reciprocating pump has minimum.

83. Specific speed of a turbine is 800. What type of turbine is this ?
 Kaplan turbine.

84. In which type of lubrication system the starting friction is low ?
 Hydrostatic lubrication.

85. At which point the cavitation is most likely to occur in a hydel plant ?
 At turbine rotor exit.

86. What is the difference between lower pair and higher pair ?
 In a kinematic pair, if the elements have surface contact when in motion, the pair is called lower pair and if elements have line or point contact the pair is called higher pair.

87. What do you understrand by inversions and how many inversions are possible in a kinematic chain having 'n' links ?
 Inversions are different mechanisms obtained by fixing different links in a kinematic chain but keeping relative motions of links unchanged with respecat to one another. A kinematic chain with 'n' links can have 'n' inversions.

88. What is the difference between basic kinematic chain and compound kinematic chain ? What is the criteria for a chain to be constrained ?
 A basic kinematic chain consists of four kinematic links and a compound kinematic chain is a constrained chain of more than four links. A chain is constrained if no. of binary joints and half of number of higher pairs is equal to 3/2 of no. of links minus 2.

89. What is the difference between a machine and a mechanism ?
 A mechanism consists of links forming a constrained kinematic chain. Its function is ba¬sically to transmit or modify motion. A machine is a mechanism but here we are concerned with forces to be transmitted and it is used to modify mechanical work.

90. In which type of motion, acaceleration is directly proportional to displacement ?
 SHM.

91. What is the function of a transducer element ?
 The function of a transducer element is to sense and convert the desired input into a more convenient and practicable form to be handled by measurement system.

92. What is the direction of tangential acceleration ?
 The direction of tangential acceleration may be same or opposite to that of angular velocity.

93. What is the number of degrees of freedom constrained in each case by the kinematic pairs.
(i) Itevolute pair, (ii) cylindrical pair, (iii) Screw pair, (iv) Spherical pair.
Ans:  (i) Revolute pair—single degree of freedom.  
        (ii) cylindrical pair—two degrees of freedom.
        (iii) Screw pair—one degree of freedom.   
        (iv) spherical pair—three degrees of freedom.

94. What is the purpose of D-slide valve in steam engines ?
 It controls the piston position for cut off of steam, for release of steam and compression position for steam in cylinder.

95. What is the purpose of Corliss valve in place of D'-slide valve in steam engine ?
 Corliss valve reduces condensation, provides independent control on admission, cut off, release and compression, and reduces driving power requirements.

96. On what factor the size of cam depends ?
 Size of cam depends on base circle.

97. If base circle diameter of cam increases, what happens to pressure angle ?
 It decreases.

98. If angular speed of cam is increased two times, how much jerk will be increased ?
 Eight times.

99. Define primary and secondary transducers ?
 A primary transducer senses a physical phenomena and converts it to an analogous output.
The analogous output is then converted into an electrical signal by secondary transducer.

100. What is the relationship between (i) axes of spin, precession, and applied gyroscopic torque and (ii) in between their planes ?
 The axes of spin, precession, and applied gyroscopic torque are contained in two planes perpendicular to each other, and planes of spin, precession, and applied gyroscopic torque in the three planes perpendicular to one another.

Interview Questions and Answers for Mechanical Engineering

1. How shear forces are incurred in fluid flow ?
Ans:  Shear forces between fluid particles and boundary walls and between the fluid particles themselves, result from the viscosity of the real fluid.

2. In laminar flow, how discharge is related to viscosity ?
Ans:  Discharge varies inversely as viscosity.

3. What is best hydraulic section ?
Ans:  Best hydraulic section is one in which for a given cross-section area, the channel section has least wetted perimeter.

4. What is best hydraulic trapezoidal section ?
Ans:  It is a half-hexagon in shape.

5. What is specific energy in a channel section ?
Ans:  It is defined as the energy head measured with respect to the channel bottom at the sec¬tion. At any section, it is equal to sum of the velocity head and the water depth at the section.

6. What is critical depth and critical flow ?
Ans:  Critical depth is the depth, at which the discharge may be delivered through the section at minimum energy.
Critical flow is the flow in open channel corresponding to critical depth.

7. What causes boundary layer separation ?
Ans:  An adverse pressure gradient.

8. What is the improtance of Nose radius ?
Ans:  Nose radius is favourable to long tool life and good surface finish. A sharp point on the end of a tool is highly stressed, short lived and leaves a groove in the path of cut.

9. At what point below free surface in a uniform laminar flow in a channel the point velocity is equal to mean velocity of flow ?
Ans:  At 0.577 depth of channel.

10. What is the value of friction factor for smooth pile when Reynolds number is approximately = 10G ?
Ans:  0.01.

11. How hydraulic grade line and free surface of open channel flow related ?
Ans:  They coincide.

12.What are the first and last elements of tool signatures ?
Ans:  Back rake angle and nose radius.

14. What is open channel flow ? Explain 4 types of open channel flows.
Ans:  Open channel flow has a free water surface which is normally subject to the atmospheric pressure.
Steady open channel flow : In this case the discharge and water depth at any section in the reach do not change with time during the period of interest.
Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time.
Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady.
Varied open channel {low : In this case the water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unstgeady (as in the case of flood waves or tidal surge).

15. When does wake occur ?
Ans:  It occurs after a separation point.

16. In straight polarity, to which terminal the electrode is connected ?
Ans:  Negative.

17. What is hydraulic radius ?
Ans:  It is the ratio of fluid flow area/shear perimeter.

18. Define flow work.
Ans:  Flow work is the amount of mechanical energy required to push or force a flowing fluid across a section boundary.

19. What do you understand by dimensional analysis ?
Ans:  Dimensional analysis is the mathematics of dimensions and quantities and provides procedural techniques whereby the variables that are assumed to be significant in a problem can be formed into dimensionless parameters, the number of parameters being less than the number of variables.

20. What is hydraulic depth for open channel flow ?
Ans:  It is the ratio of area and the top width of the channel section.

21. Which welding set will you select for welding both ferrous and non ferrous materials.
Ans:  D.C. generator set.

22. Which welding process is a combination of arc welding and gas welding processes?
Ans:  Atomic hydrogen welding.

23. What is hydraulic jump ?
Ans:  It is a natural phenomenon in open channel. It is an abrupt reduction in flow velocity by means of a sudden increase of water depth in the down stream direction. Through a hydraulic jump, and high-velocity supercritical flow is changed to a low-velocity subcritical flow.

24. What is gradually varied flow ?
Ans:  The changes in water depth in the open channel take place very gradually with distance. Depending on the channel slope, the surface conditions, the sectional geometry, and the discharge, these may be classified into five categories : steep channel, critical channel, mild channel, horizontal channel, and adverse channel.

25. Explain 5 types of channels.
Ans:  Steep channel : In this case normal depth < critical depth.
Critical channel   : In this case normal depth = critical depth.
Mild channel       : In this case, normal depth > critical depth.
Adverse channel    : In this case, the slope of channel bed < 0
Horizontal channel : In this case, the slope of channel bed = 0.

26. Mention two major differences between shaper and planer ?
Ans:            Shaper                                   Planer
(a)    The cutting tool reciprocates     (a) Work reciprocates
(b)    The work is stationary              (b) Tool is stationary
(c)    Meant for small work pieces     (c) Meant for large work pieces
(d)    Only lighter cut can be taken    (d) Heavy cuts can be taken
(e)    Tools are smaller in size           (e) Tools are bigger in size

27. Differentiate between drilling and reaming ?
Ans:              Drilling                                                              Reaming
(a)    It is the operation of initiating hole                (a)  Reaming is the operation of finishing and
                                                                             sizing a drilled/bored hole
(b)    It can be done at relatively high speeds        (b)  It should be done only at slow speeds
(c)    Larger chips are produced                          (c)   Less chips are produced
(d)     Drill has only two flutes                              (d)   Reamer has more than 4 flutes
(e)     Drill has chisel edge                                    (e)   Reamer has a bevel edge

28. What is similarity between normal shock wave and hydraulic jump ?
Ans:  Both are analogous and irreversible.

29. For what purpose chills are used in moulds ?
Ans:  Chills are used to achieve directional solidification.

30. What is tumbler gear mechanism ?
Ans:  Tumbler gear mechanism is a mechanism consisting of number of different sized gears keyed to the driving shaft in the form of cone and is used to give the desired direction of motion of the lathe spindle.

31. What is relative roughness of pipe ?
Ans:  It is the ratio of the size of the surface imperfections to the inside diameter of the pipe.

32. What is conicity ?
Ans:  The ratio of the difference in diameter of the taper to its length is termed conicity.

33. Under what condition the effect of compressibility of fluid can be neglected ?
Ans:  When Mach number is less than 0.4.

34. For which type of flow the velocity distribution in a pipe is parabolic.
Ans:  For uniform laminar flow.

35. What is the relationship between center line velocity and average velocity for a laminar flow in a pipe ?
Ans:  Average velocity = 1/2 centre line velocity.

36. On which factor the friction factor for a smooth pipe in turbulent flow depends ?
Ans:  Reynolds number.

37. What do you understand by pipe branchings ?
Ans:  When water is brought by pipes to a junction where more than two pipes meet, them the total amount of water brought by pipes to a junction must always be equal to that carried away from the junction by other pipes, and all pipes that meet at the junction must share the same pressure at the junction.

38. What is pipe networks and what are the condition for network ?
Ans:  Pipe network comprises a number of pipes connected together to form loops and branches. For a network,
(i) at any junction, Y.Q = 0 and
(ii) between any two junctions the total head loss is independent of the path taken.

39. What is Hardy-Cross Method ?
Ans:  It is a commonly used computer program for a pipe network.

40. Explain water hammer.
Ans:  The force resulting from changing the speed of the water mass (say in a pipe due to sudden change of flow rate) may cause a pressure rise in the pipe with a magnitude several times greater
than the normal static pressure in the pipe. Pressure head caused by water hammer = C (V - velocity in pipe, C = celerity).

41. What happens to impurities in centrifugal casting ?
Ans:  They get collected at the center of the casting.

42. Define the terms hydraulic similitude and dimensional analysis.
Ans:  Hydraulic similitude is the principle on which the model studies are based.
Dimensional analysis is the analysis of the basic relationship of the various physical quantities involved in the static and dynamic behaviors of water flow in a hydraulic structure.

43. Explain the difference between geometric similarity, kinematic similarity and dynamic similarity.
Ans:  Geometric similarity : It implies similarity of form. The model is a geometric reduction of the prototype and is accomplished by maintaining a fixed ratio for all homologous lengths between the model and the prototype.
Kinematic similarity : It implies similarity in motion. Kinematic similarity between a model and the prototype is attained if the homologous moving particles have the same velocity ratio along geometrically similar paths. It involves the scale of time as well as length.
Dynamic similarity : It implies similarity in forces involved in motion.

44. Define Reynolds law ?
Ans:  When the inertial force and the viscous force are considered to be the only forces governing the motion of the water, the Reynolds number of the model and the prototype must be kept at the same value.

45. When a built up edge is formed while machining ?
Ans:  While machining ductile materials at high speed.

46. On what factor the friction factor for a rough pipe in turbulent flow depends ?
Ans:  Relative roughness.

47. What is unit power of a turbine ?
Ans:  PHP12.

48. How cavitation causes damage ?
Ans:  In a a closed system (pipelines, or pumps), water vaporises rapidly in regions where the pressure drops below the vapour pressure. This phenomenon is called cavitation. The vapour bubbles formed in cavitation usually collapse in a violent manner, which may cause considerable damage to the system.

49. In milling process, how the arbor torque can be smoothend ?
Ans:  Arbor torque can be smoothened by increasing number of teeth, using higher spiral angle of teeth, using higher cutting depth.

49. What are webs in a twist drill ?
Ans:  Webs are the metal column in the drill which separates the flutes.

50. What is bluff body ?
Ans:  It is a body with such shape that the flow is separated much ahead of its rear end resulting in a large wake, the pressure drag being much greater than the friction drag.

51. What is bulk modulus ?
Ans:  It is the ratio of hydrostatic stress to volumetric strain within the elastic limits.

52. Define boundary layer.
Ans:  It is the fluid layer in the neighborhood of a solid boundary where the effects of fluid friction are predominant.

53. What is creep flow ?
Ans:  It is flow at very low Reynolds number where viscous forces are larger than the inertia forces.

54. What is Torricellis theorem ?
Ans:  According to it velocity of jet flowing out of a small opening is proportional to the square root of head of liquid above it.

55. How does cavitation manifest itself in a centrifugal pump ?
Ans:  Usual symptoms of cavitation of pump are noise, vibration, a drop in head and capacity with a decrease in efficiency, accompanied by pitting and corrosion of the impeller vanes.

56. What happens if centrifugal pump is operated at excessive speeds ?
Ans:  When a pump is operated at excessive speeds, the differential pressure developed increases and causes a powerful pulsating vacuum on the underside of the blade tips and each particle of water is pulled away from the blade, taking away with it a small particle of metal, producing pitting/grooved effect. Repeated erosive action results in complete honey combing and total destruction of blade, with resultant loss in pump performance.

57. On what parameters the head developed by a centrifugal pump depends ?
Ans:  It depends upon the impeller diameter and its rotative speed.

58. Which factors determine the selection of electrolyte for electrochemical machining process ?
Ans:  Electrolyte should be chemically stable and have high electrical conductivity.

59. What is the disadvantages of centrifugal pump having very low specific speed ?
Ans:  For a.centrifugal pump having very low specific speed, the impeller diameter is large and narrow having excessively high disc friction and excessive hydraulic losses.

60. On what factors the efficiency of pump depends ?
Ans:  Efficiency of a pump (centrifugal) depends on the size, speed, and proportions of the impeller and casing.

61. On what factors the cavitation in centrifugal pumps is dependent ?
Ans:  Cavitation in centrifugal pumps depends on the velocity of water entering tne impeller and on the relatiave velocity of the impeller blades where the water is picked up.

62. What are the losses in a centrifugal pump ?
Ans:  The losses in a centrifugal pump are : Friction losses due to eddies in flow, leakage, friction loss due to rotation of impeller in chamber of water, gland and bearing power losses.

63. What should be done to avoid cavitation in pumps ?
Ans:  In order to avoid cavitation, the suction lift and the operating speed must be carefully chosen.

64. What will happen if speed of reciprocating pump is increased ?
Ans:  If speed of a reciprocating pump is increased beyond a limit, then atmospheric pressure would be insufficient to force water into the pump at the same speed as the piston. This would a break in the continuity of the water in suction pipe (cavitation) and give rise to vibration, noise, and chemical attack by any dissolved gases which may be released from the water owing to the high vacuum and the breaking of the water column.

65. What is the order of efficiency of cenetrifugal and reciprocating pumps ?
Ans:  The efficiency of centrifugal pump is of the order of 45% whereas that of reciprocting pump is around %.

66. What are the basic operations performed in a slotter ?
Ans:  The different operations done in slotter are :
1. Machining grooves   
2. Machining cylindrical surface      
3. Machining irregular profiles.

67. How the positive displacement is obtained in rotary pumps ?
Ans:  Positive displacement in rotary pumps is achieved in two ways :
(i) A rotor carries radially adjustable vanes, the outer tips of which are constrained by a circular casing, whose centre is remote from that of the rotor.
(ii) Various combinations of gears, lobes, helices, etc. within a casing arranged so that the lobes or teeth attached to each rotor pass in sequence through the same pumping space.

68. How a slotter differs from shaper ?
Ans:          Slotter                                        Shaper
(a)  Ram reciprocates vertically          (a) Ram reciprocates horizontally
(b)  It has a circular table                  (b) It has a rectangular table
(c)  Suited for machining internal surfaces   (c) Suited for machining external surfaces
(d)  Table can take less load                  (d) Table can take much load

69. Under what condition the flow and power of pump vary as square of the size ?
Ans:  The flow and power vary as size2 when the geometric size changes as inverse of change of speed.

70. How the incidence of cavitation detected ?
Ans:  The incidence of cavitation is detected by the following in order of appearance.
(i)   stroboscopic observation of bubble appearance and size
(ii)  sensitive acoustic tests of cavitation noise
(iii) reduction of efficiency and/or head of 3%.

71. How cavitation erosion is assessed ?
Ans:  Cavitation erosion is assessed by depth of attack or weight of metal removed.

72. At which temperature the cavitation erosion is negligible and why ?
Ans:  Cavitation erosion is negligible at above 300°C because the water and steam have same densities at critical temperature of 374°C and thus there is no volume change or bubble collapse in the vicinity of this range.

73. What is an arbor ?
Ans:  An arbor is an accurately machined shaft for holding and driving the arbor type cutter. It is tapered at one end to fit the spindle nose and has two slots to fit the nose keys for locating and driving it.

74. For a body to float in stable equilibrium where the e.g. should be located w.r.t. metacentre ?
Ans:  e.g. should be below metacentre.

75. What is the condition for a flow to be fully developed through a pipe ?
Ans:  Ratio of maximum velocity to average velocity should be 2.

76. When a fluid is moving with uniform velocity, whether the pressure of fluid will depend on its depth and orientation ?
Ans:  No.

77. How much is the vertical component of force on a curved surface submerged in a static liquid ?
Ans:  It is equal to weight of the liquid above the curved surface.

78. On which factors depends the friction factor in a rough turbulent flow in a pipe?
Ans:  It depends on pipe diameter and the condition of the pipe.

79. What does the realisation of velocity potential in fluid flow indicate ?
Ans:  It indicates that flow is irrotational.

80. What is the difference between potential flow and creep flow ?
Ans:  Potential flow assumes viscous forces to be zero but same is considered larger than inertia forces in creep flow.

81. For which application Mach number and Froude numbers are significant ?
Ans:  Mach no. is significant in the study of projectiles and jet propulsion. Froude number is significant in the study of ship hulls.

82. What is the difference between geometric, kinematic, and dynamic similarities between model and prototype ?
Ans:  Geometric similarity is mainly for same shape for model and prototype, kinematic similarity is concerned with stream line pattern, whereas dynamic similarity concerns the ratio of forces.

83. A body is floating in water. If it is displaced slightly then about which point it will oscillate.
Ans:  It will oscillate about centre of buoyancy.

84. Why uniform ramming is considered desirable in green sand moulding process ?
Ans:  Uniform ramming results in greater dimensional stability of a casting.

85. On what account the friction drag is experienced ?
Ans:  Friction drag is experienced on separation of boundary layer.

86. What is the characteristic of centrifugally cast components ?
Ans:  These have fine grain structure with high density.

87, Under what condition the separation of flow occurs ?
Ans:  When pressure gradient changes abruptly.

88. What is the criterion for shaping of streamlined body ?
Ans:  It is shaped to suppress the flow separation about the body and to shift the boundary layer separation to near most part of body to reduce the wake size.

89. What do you understand by entrance length and what is its value for turbulent flow in smooth pipe ?
Ans:  Entrance length of flow is the initial length in which the flow develops fully such that the velocity profile remains unchanged downstream. For turbulent flow in smooth pipe, entrance length is taken as 50 x diameter of pipe.

90. Explain the difference between friction drag and pressure drag.
Ans:  Friction drag is the drag force exerted by a fluid on the surface due to friction action when
the flow occurs past a flat surface at zero incidence. Pressure drag is the additional drag force on
account of the differences of pressure over the body surface when flow occurs past a surface which is
not everywhere parallel to the fluid stream. Pressure drag depends upon separation of bondary layer
and the size of wake. Friction drag is due to shear stresses generated due to viscous action.

91. What do you understand by choking in pipe line ?
Ans:  When specified mass flow is not able to take place in a pipe line.

92. What is the difference between streamline body and bluff body ?
Ans:  In streamline body the shape is such that separation in flow occurs past the nearmost part of the body so that wake formed is small and thus friction drag is much greater than pressure drag. In bluff body the flow gets separated much ahead of its rear resulting in large wake and thus pressure drag is much greater than the friction drag.

93. What is the difference between dressing and trueing of a grinding wheel ?
Ans:  Dressing is the process used to clear the cutting surface of the grinding wheel of any dull grits and embedded swarf in order to improve the cutting action. Trueing is the process employed to bring the wheel to the required geometric shop and also to restore the cutting action of a worn wheel.

94. Whether hard grade or softer grade is required for internal grinding than external grinding?
Ans:  Softer graders of wheel are required for internal grinding than for external grinding.

95. How is the velocity profile and stress distribution due to laminar flow of an incompressible flow under steady conditions in a circular pipe.
Ans:  Velocity profile is parabolic with zero velocity at boundary and maximum at the centre. Shear stress distribution is linear, being maximum at boundary and zero at centre.

96. Where the maximum velocity occurs in open channels ?
Ans:  Near the channel bottom.

97. Define hydraulically efficient channel cross section.
Ans:  The shape of such section is that which produces minimum wetted perimeter for a given area of flow and carries maximum flow.

9. What is follower rest ?
Ans .For slender work a travelling or follower rest is used. This fits on the lathe - saddle and travels to and fro with it. By this means support is constantly provided at the position of cut. Thus the work piece being turn is rigidly held against the tool.

99. What is the meaning of the term sensitive drill press ?
Ans:  A sensitive drilling press is a light, simple, bench type machine for light duty working with infinite speed ratio.

100. Why carburised machine components have high endurance limit ?
Ans:  In carburised machine components, the process of carburisation introduces a compressive layer on the surface and thus endurance limit is increased.

Interview Questions for Mechanical Engineering Set5

1. What is anisotropy ?
Ans:  The phenomenon of different properties in different directions is called anisotropy.

2. What is vapour pressure and when it becomes important ?
Ans:  Vapour pressure is the partial pressure created by the vapour molecules when evaporation takes place within an enclosed space. It becomes important when negative pressures are involved.

3. Explain absolute viscosity ?
Ans:  It is the ratio of shear stress and the gradient of velocity with distance between a fixed plate and moving plate (Its unit is Pa . s).

4. Define surface tension ?
Ans:  Surface tension of a liquid is the work that must be done to bring enough molecules from inside the liquid to the surface to form one new unit area of that surface. (Its unit is Nm/m2 or N/m).

5. What is capillarity and when liquid rises or falls ?
Ans:  Capillarity : The rise or fall of a liquid in a capillary tube caused by surface tension. The magnitude of rise or fall depends on the relative magnitudes of the cohesion of the liquid and adhesion of the liquid to the walls of the containing vessels. Capillarity is of importance in tubes smaller
than 10 mm diameter.
Rise of liquid : Liquids rise (in capillary tube) when they wet and adhesion of the liquid to the walls is greater than the cohesion of the liquid.
Fall of liquid : Liquids fall (in capillary tube) when they do not wet and the cohesion of the liquid is greater than the adhesion of the liquid to the walls.

6. What is the difference between perfect and real fluids ?
Ans:  Perfect fluids are treated as if all tangential forces created by friction can be ignored.
Real fluids refer to the cases in which friction must properly be taken into account.

7. Which factors affect tool size ?
Ans:  Following factors influence tool size :
1.    Process variable (speed, feed and depth of cut)
2.    Tool material
3.    Tool geometry
4.    Work piece material, its hardness, microstructure and surface condition
5.    Cutting conditions.

8. When the motion of fluid is fully known ?
Ans:  The motion of a fluid is fully known when the velocity of each of its particles can be specified.

9. Define fluid.
Ans:  A fluid is a substance that can't remain at rest under the action of any shear force.

10. How is the size of a vertical boring machine designated ?
Ans:  The specifications of vertical boring machine are :
(i) Column height  
(ii) Table size  
(iii) Floor area
(iv) Weight of the job  
(v) Spindle of the motor.

11. What do you mean by drill sleeve and a drill socket ?
Ans:  The drill sleeve is suitable for holding only one size of shank. If the taper shank of the tool is smaller than the taper in the spindle hole, a taper sleeve is used.
When the tapered tool shank is larger than the spindle taper, drill sockets are used to hold the tools. Drill sockets are much longer in size than the drill sleeves.

12. What is nonbarotropic fluid ?
Ans:  Fluid such as air for which the density is not a single-valued function of the pressure (aerostatics).

13. On account of which property, the falling drops of rain acquire superical shape.
Ans:  Surface tension.

14. How you can definte standard atmospheric pressure ?
Ans:  By international agreement, the standard atmospheric pressure is defined as 101.325 kN/m2.

15. What do you understand by acoustic velocity ?
Ans:  Accoustic velocity is the speed of a small pressure (sound) wave in a fluid.

16. Explain the difference between centipoise and centistoke ?
Ans:  Centipoise is the unit of dynamic viscosity. It is equal to 1/100 of poise, and poise = 0.1 Pa . s. Value of dynamic viscosity of water at 20°C is approximately equal to 1 Centipoise.
Centistoke is the unit of kinematic viscosity and is equal to 1/100 x stoke. Stoke is defined as 1 square centimeter per second.

17. What is saybolt seconds universal ?
Ans:  Saybolt Seconds Universal (SSU) is the unit of viscosity and is equal to the time required for a gravity flow of 60 cc through saybolt universal viscometer.

18. Explain difference between cohesion, adhesion and capillarity ?
Ans:  Cohesion is the attraction of like molecules.
Adhesion is the attraction of unlike molecules for each other.
Capillarity is the elevation or depression of a liquid surface in contact with a solid.

19. Differentiate between gear hobbing and gear shaping with reference to various relative motions and applications.
Ans:  Gear hobbing is a continuous indexing process in which both cutting tool (a hob) and work piece rotate in a constant relationship while the hob is being fed into work. Hob is also imparted a radial feed.
Gear shaping uses a pinion type of cutter which is reciprocated with required cutting speed along the face of workpiece and is gradually fed radially to plunge. Continuous generation motion is obtained by feeding cutter to full depth and rotating the cutter and workpiece slowly.

20. What is bulk modulus of elasticity ?
Ans:  It represents the compressibility of a fluid. It is the ratio of the change in unit pressure to the corresponding volume change per unit of volume.

21. What is is entropic exponent ?
Ans:  It is the ratio of the specific heat of a gas at constant pressure to the specific heat at constant volume.

22. The best shape of a runner in sand casting is an inverted frustum of a cone why ?
Ans:  Tapered shape with bigger diameter at top and smaller at bottom ensures avoidance of entrainment or absorption of air/gases into the metal while passing through the runner.

23. Explain difference between ideal fluid and non-newtonian fluid.
Ans:  Ideal fluid is one for which resistance to shearing deformation is zero.
Non-netwtonian fluids deform in such a way that shear stress is not proportional to the rate of shearing deformation.

24. Explain the difference between poise and stoke.
Ans:  Poise is the unit of viscosity in CGS unit and is measured in dyne sec/cm2.1 poise = 10_1 Pa s.
Stoke is the unit of kinematic viscosity in CGS units and is measured in cm2/s.

25. How does the pressure in an isothermal atmosphere behave ?
Ans:  It increases exponentially with elevation.

26. The centre of pressure for a plane surface immersed vertically in a static liquid compared to centroid of area is always ... ?
Ans:  Below.

27. What is buoyant force equal to ? Define centroid of the area.
Ans:  Volume of liquid displaced.
Centroid of the area : The point at which the area might be concentrated and still leave un¬changed the first moment of the area around any axis. It is also the centre of gravity.

28. Define vapour pressure and on what parameters it depends ?
Ans:  The pressure exerted when a solid or liquid is in equilibrium with its own vapour is called vapour pressure. It is a function of the substance and its temperature.

29. Explain the difference between steady flow, one dimensional flow, two dimensional flow and three dimensional flow ?
Ans:  If at every point in the continuum, the local velocity and other fluid property, remains unchanged with time, it is referred to as steady flow.
One dimensional flow is one in which a line is necessary to describe the velocity profile.
Two dimensional flow is one in which an area is necessary to describe the velocity profile.
Three dimensional flow is one in which a volume is necessary to describe the velocity profile.

30. What is aquifer and explain difference between confined and unconfined aquifers.
Ans:  Groundwater occurs in permeable, water-bearing geologic formations known as aquifers.
Confined aquifer : It is a relatively high-permeable, water-bearing formation.
Unconfined aquifer : It is a water-bearing formation with a free water table, below which the soil is saturated.

31. What do you understand by flurial hydraulics ?
Ans:  The channels may be classified as rigid boundary or mobile boundary channels. Mobile boundary channels include rivers and unlined alluvial canals, the boundaries of which are made of loose soil which can be easily eroded and transported by flowing water. The study of flow of water in mobile boundary channels is dealt in flurial hydraulics.

32. By which instruments the shear stress in fluids can be measured directly ?
Ans:  By Stanton tube or Preston tube.

33. On what factors does the pressure at a point as a static mass of liquid depends upon?
Ans:  Specific weight of liquid and the depth below the free liquid surface.

34. What is the difference between hoop or longitudinal tension and circum-ferencial tension ?
I     Ans:  Hoop tension is created in the walls of a cylinder subjected to internal pressure. For thin walled cylinder (t < 0.1 d), hoop stress = pressure x radius/thickness.
Longitudinal tension in thin-walled cylinders closed at the ends is equal to half the hoop tension.

35. How much force is exterted by liquid ?
Ans:  Force exerted by a liquid on a plane area A is equal to the product of the unit weight pg of the liquid, the depth hcg of the centre of gravity of the area, and the area.

36. State standard point angle and helix angle of a twist drill.
Ans:  Standard point angle of twist drill is 118° and helix angle varies from 16° to 30° depending as diameter of hole.

37. Explain the difference between horizontal and vertical components of hydrostatic force ?
Ans:  The horizontal component of the hydrostatic force on any surface is equal to the normal force on the vertical projection of the surface and acts through the center of pressure for the vertical projection.
Vertical component of the hydrostatic force on any surface is equal to the weight of the volume of liquid abaove the area and passes through the e.g. of the volume.

38. What should be diameter of capillary tube to avoid correction for effect of capillarity in manometer ?
Ans:  Greater than 6 mm.

39. How much hydrostatic pressure acts on a curved surface ?
Ans:  The horizontal component of the total hydrostatic pressure force on any surface is always equal to the total pressure on the vertical projection of the surface, and can be located through the center of pressure of this projection.
The vertical components of the total hydrostatic pressure force on any surface is always equal to the weight of the entire water column above the surface extending vertically to the free surface, and cvan be located through the cemntroid of this column.

40. How much is the horizontal component of force on a curved surface ?
Ans:  Force on a vertical projection of the curved surface.

41. State Archimedes principle.
Ans:  Any weight, floating or immersed in a liquid, is acted upon by a buoyant force equal to the weight of the liquid displaced. This force acts through the center of buoyancy, i.e. the e.g. of the displaced liquid.

42. What do you understand by center of buoyancy ?
Ans:  Center of buoyancy is the center of gravity of the displaced liquid and buoyant force acts through it.

43. How one can establish stability of submerged body and floating body ?
Ans:  A submerged body floats in stable equilibrium when the center of gravity of the body lies directly below the center of buoyancy.

44. What is neutral equilibrium ?
Ans:  A submerged body is in neutral equilibrium for all positions when the center of gravity of body coincides with the center of buoyancy.

45. On what factors the stability of floating objects depends ?
Ans:  Stability of floating objects depends upon whether righting or overturning moment is developed when the center of gravity and center of buoyancy move out of vertical alignment due to the shifting of position of center of buoyancy.

46. State two products each produced by forward extrusion and reverse impact extrusion.
Ans:  Two examples of products made by direct extrusion are : gear profile, solder wire.
Two examples of reverse impact extrusion are : Short tubes of soft alloys, tooth paste containers.

47. What are the best geometrical shapes suggested for sheet metal drawing and spinning?
Ans:  Cup shape is best suited by drawing operation. Conical shape is easiest to produce by spinning operation.

48. What are the conditions for stability of buoyant bodies ?
Ans:  A floating body is stable if the center of gravity is below the metacentre.
A submerged body is stable if the center of gravity is below the center of buoyancy.

49. Define pipe flow ?
Ans:  It refers to full water flow in closed conduits of circular cross section under a certain pres¬sure gradient.

50. How much is vertical component of pressure force on a submerged curved surface ?
Ans:  The weight of liquid vertically above the curved surface.

51. Multiple coated, disposable carbide tips have more-or-less replaced brazed carbide tipped tools in CNC applications. Why ?
Ans:  Disposable tips are usually indexable type and have a number of cutting edges. Very convenient gripping devices for holding such inserts on tool holders are available. A wide variety of ready made inserts are available which require no grinding or adjustment.

52. State, sequentially elements of a canned CNC drilling cycle.
Ans:  Canned cycles are fixed cycles for general sequences of operations. For drilling operation, sequence of operations will be movement of drill or workpiece to position of actual drilling, movement of drill downwards till it is in the proximity of workpiece, then movement of drill at desired feed rate to sufficient depth of hole, retracting the drill above the workpiece.

54. Explain the difference between one and two dimensional flow ?
Ans:  True one-dimensional flow occurs when the direction and magnitude of the velocity at all points are identical. Velocities and accelerations normal to the streamline are negligible. Two dimensional flow occurs when the fluid particles, move in planes or parallel planes and the stream-line patterns are identical in each plane.

55. What is the difference between irrotational and rotational flow ?
Ans:  Irrotational flow : An ideal fluid flow in which no shear stresses occur and hence no torques exist. Rotational motion of fluid particles about their own mass centers can not exist. It can be represented by a flow net.
Rotational flow occurs when the velocity of each particle varies directly as the distance from the center of rotation.

56. Explain the difference between steady and unsteady flows.
Ans:  In steady flow, at any point, the velocity of successive fluid particles is the same at successive periods of time.
Flow is unsteady when conditions at any point in a fluid change with time,

57. What is the difference between uniform and non-uniform flows ?
Ans:  Uniform flow occurs when the magnitude and direction of the velocity do not change from point to point in the fluid.
Non uniform flow occurs when velocity, depth, pressure, etc. change from point to point in the fluid flow.

58. Explain the difference between stream lines and stream tube.
Ans:  Stream lines are imaginary curves drawn through a fluid to indicate the direction of motion in various sections of the flow of the fluid system. There can be no flow across a streamline at any point.
Stream tube represents elementary portions of a flowing fluid bounded by a group of stream¬lines which confine the flow.

59. What is the advantage of independent jaw chuck ?
Ans:  Irregular job can be fixed.

60. Define vorticity ?
Ans:  It equals twice the angular velocity.

61. What is irrational How ?
Ans:  If a flow is uniform in one region (without rotation), this property is conserved as the fluid moves into a region of space where the motion is not uniform, and the flow is termed irrotational flow.

62. What is one-seventh power law ?
Ans:  According to one-seventh power law of turbulent, velocity variation corresponds to a much favoured velocity profile and the mean velocity increases as the one-seventh power of the distance from the boundary wall.

63. Mention the major difference between drilling and boring ?
Ans:                Drilling                                          Boring
(a)    It is the operation of initiating a hole        Boring is the operation of enlarging a drilled hole
(b)    It can produce only standard holes         We can produce non-standard hole
(c)    Drill is a multi point tool                          A single point tool is used

64. What is the magnitude of buoyant force and where does the line of action of buoyant force act ?
Ans:  It is equal to the volume of the liquid displaced. The line of action of buoyant force acts through the centroid of the displaced volume of the fluid.

65. What is metacentre ?
Ans:  Metacentre is the point at the intersection of the buoyancy with the vertical axis of the body.

66. Define Prandtl's pitot-static tube.
Ans:  It is a combination of pressure probe and pitot tube. It is widely used for pressure measurements in wind-tunnel installations.

67. Define the term fluid friction.
Ans:  The deformation of real fluids is resisted by forces caused by internal friction or viscosity. Viscosity is that property of a real fluid which creates shear forces (fluid friction) between two fluid selements.

68. Why are hydrodynamic bearings used for grinding machines in preference to ball or roller bearings ?
Ans:  Hydrodynamic bearings are more suitable at high speed, better tolerances, quiet operation, higher capacity to withstand shock, lesser space requirement, better life under fatigue conditions etc.

69. Distinguish between a jig and fixture.
Ans:  Jig clamps and locates parts in positive manner and guides cutting tools (drills, reamers, taps etc). Fixture is bolted or fixed securely to the machine table so that work is in correct location ship to the cutter. Fixtures are used for mass milling, turning and grinding, etc.

70. State the similarities and differences between a fixture and a jig.
Ans:  Both jig and fixture positively locate, hold and clamp the workpiece. Jigs guide the tool for drilling etc but fixture has no facility to guide the cutting tools. Jigs are used for drilling etc and fixture for mass milling, turning, grinding, etc.

71.Explain the difference between relative density, viscosity and kinematic viscosity ?
Ans:  Relative density is that pure number which denotes the ratio of the mass of a body to the mass of an equal volume of a substance taken as a standard. This standard is usually water (at 4°C) for solids and liquids, and air free or C02 or hydrogen (at 0°C and 1 atmosphere = 1.013 x 105 Pa pressure) for gases.
Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force. It is due primarily to interaction between fluid molecules.
Kinematic viscosity is the ratio of absolute viscosity and mass density. (Its unit is m2/s).

72. A right hand helical gear is being cut on a milling machine. What changes in machine settings have to be made to cut a left hand helical gear of same pitch and number of teeth ?
Ans:  For cutting right hand helical gear right side of milling table is tilted up from normal position by the helix angle. For cutting left hand helical gear, right side of table needs to be tilted down at helix angle, all other settings remaining unchanged.

73. Explain what you understand by the term hydrostatic paradox ?
Ans:  Hydrostatic paradox is the phenomenon that the floor load of water in vessels of different shapes carrying water at same level depends only on the area of the bottom surface and not on the shape of the vessel.

74. Define buoyancy in brief.
Ans:  Buoyancy is the vertical force exerted on the body by the fluid at rest. The buoyancy of a submerged body in a fluid at rest is equal to the weight of the fluid displaced by the body and it acts upward through the center of gravity of the displaced volume (the center of buoyancy).

75. What is the necessary condition for a body to float in stable equilibrium ?
Ans:  Meta center should be above the center of gravity.

76. If liquid rotates at constant angular velocity about a vertical axis as a rigid body, then how its pressure varies at various radial distances ?
Ans:  As square of the radial distance.

77. How does the velocity vary along radius in a few vortex ? .
Ans:  It decreases with radius.

78. What type of flow will occur when liquid discharges at constant rate through a long, straight tapering pipe ?
Ans:  Steady non-uniform flow.

79. What does continuity equation represent ?
Ans:  It relates mass rate of flow along a stream tube.

80. Under what condition steady flow occurs ?
Ans:  When conditions do not change with time at any point.

81. Why a drill can not drill deeper than its flute length ?
Ans:  If flute submerges in a drilled hole, the chips disposal passage is blocked and the drill will get jammed in the hole.

82. When do you recommend the use of straight fluted drill ?
Ans:  Drills used for brass and other soft materials and thin sheets need not be provided with any helix angle, to prevent the lips digging into the workpiece.

83. Explain velocity distribution for laminar and turbulent flows.
Ans:  In case of laminar flow, the velocity distribution follows a parabolic law of variation. The maximum velocity at center of pipe is twice the average velocity. For turbulent flow, more uniform velocity distribution results.

84. In which type of flow the stream lines, streak lines and path lines are identical ?
Ans:  In steady flow.

85. Under what condition a drill may not cut ?
Ans:  When the cutting lips are not provided with clearance angles. It will cut if 12° clearance angle is ground.

86. Some drills have straight shanks and some have tapered shank. Why ?
Ans:  Small drills (less than 12 mm diameter) are provided with straight shanks which can be held in Dniren chucks. Bigger drills have tapered shank using self holding Morse tapers which prevent gravitational fall of drill.

87. What are the main factors that are responsible for the formation of built up edge ?
Ans:  The main factors that are responsible for the formation of built up edge are :
1. Extreme pressure in the cutting zone  
2. High friction in the tool chip interface
3. High local temperature.

88. In which type of flow the Navier-strokes equation is useful ?
Ans:  Viscous flow.

89. Explain the difference between energy line and hydraulic grade line ?
Ans:  The energy line is a graphical representation of the energy at each section.
Hydraulic grade line lies below the energy line by an amount equal to the velocity head at the section.

90. What is the characteristic of equipotential line ?
Ans:  It has no velocity component tangent to it.

91. How specific cutting pressure behaves with feed rate and what conclusion can be drawn from this ?
Ans:  As feed rate increases, the specific cutting pressure decreases. It leads to conclude that feed rates be maximised in metal cutting process.

92. What is hydraulically rough pipe ?
Ans:  When Reynolds number is very small, friction factor f becomes independent of the Reynolds number and depends only on the relative roughness height. Such a pipe behaves as hydraulically rough pipe.

93. What are the qualities of ideal tool material ?
Ans:  It should be hard to resist flank wear and deformation, have high toughness to resist fracture, be chemically inert to the workpiece, be chemically stable to resist oxidation and dissolution, and have good resistance to thermal shocks.

94. What are the factors to be considered while evaluating the machinability ?
Ans:  1. Tool life  
     2. Rate of metal removal  
     3. Power required
     4. Surface texture and size of component  
     5. Temperature of tool (or) chip.

95. Which equation is satisfied by ideal or real, laminar or turbulent flow ?
Ans:  Continuity equation.

96. How to judge the unsatisfactory performance of cutting tool ?
Ans:  Unsatisfactory performance of cutting tool leads to loss of dimensional accuracy, increase in surface roughness and increase in power requirements.

97. What are the criteria for judging machinability ?
Ans:  Cutting speed, tool life, surface finish, cutting force/energy required, teasperature rise at cutting point.

99. What is critical velocity ?
Ans:  It is the velocity below which all turbulence is damped out by the viscosity of the fluid.

100. What is laminar flow ?
Ans:  In laminar flow the fluid particles move along straight, parallel paths in layers or laminae. Laminar flow is governed by the law relating shear stress to rate of angular deformation i.e. the product of the viscosity of the fluid and velocity gradient.