Elements of Rigid Body Dynamics Interview Questions and Answers:

1. What are the common types of plane motion of rigid bodies?


  • Translation
  • Rotation
  • General plane motion

2. Define Translation.

Ans. It is the motion of a rigid body if an imaginary straight line drawn on the body remains parallel to its original position during the motion.

3. Define Curvilinear Translation.

Ans. The path described by the particle is a curved one during motion then it is said to be curvilinear translation.

4. What is meant by Rotation?

Ans. It is defined as the motion of a rigid body in which all the particles of the rigid body move in a concentric circular path.

5. Define General plane motion.

Ans. A rigid body is to be under general plane motion if it under goes translation and rotation simultaneously.

6. What is meant by angular velocity?

Ans. Angular velocity is defined as the rate of change of angular displacement.

7. Define angular acceleration.

Ans. It is defined as the rate of change of angular velocity.

8. Define uniform angular velocity.

Ans. If the particle receives equal increments of angular displacement on a circular path, during equal intervals of time, it is said to have an uniform angular velocity.

9. Give examples for plane motion of rigid bodies.


  • Rolling of wheel without slipping
  • Four bar mechanism
  • Reciprocating engine mechanism

10. Define Instantaneous centre of rotation.

Ans. In rotation of rigid bodies, it is possible to locate a point in the plane which has zero velocity at any instant and hence the plane motion of other points may looked as pure rotation about this point. Such point is called as Instantaneous Centre of rotation.

11. What are the characteristics of Instantaneous centre?


  • It may be located inside or outside the body
  • The location of instantaneous centre changes at every instant and the path traced by it is called centrode.
  • The instantaneous centre is having no velocity.

12. Define Coriolis Acceleration.

Ans. It is defined as the acceleration of a slider with respect to the surface (or) rod it is sliding, it is having a magnitude of 2υω.

13. What are the techniques used in kinetics of rigid bodies?


  • D’ Alembert’s principle
  • Impulse momentum equation
  • Work energy method

14. What are the forces having no work?
  • Reaction of the surface on a body when it moves horizontally and surface is frictionless.
  • Friction force F acting at the point of contact when the body rolls without slipping on a horizontal or inclined plane.

15. Give examples to D’ Alembert’s principle which is applicable to rotary motion.
  • Rotation of a pulley due to weight attached to one end of a string.
  • Rotation of a pulley due to weights attached to the two ends of a string.
  • Rotation of a pulley due to weights one hanging free and the other lying on a horizontal plane.

16. Define centre of percussion.
Ans. The centre of oscillation or centre of percussion is the point in the body, such that if a blow is given at that point it will not produce an impulse on the body.

17. State the principle of conservation of energy in a rigid body.
The sum of kinetic energy and potential energy of a rigid body under the action of conservative forces remains constant.
Initial Kinetic energy + Initial potential energy = Final kinetic energy + Final potential energy

18. State the principle of impulse and momentum of a rigid body in plane motion.
Initial angular momentum of rigid body + Impulse = Final Angular momentum of rigid body.