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.