Question

Which of the following statements for a rigid object undergoing pure translational motion are false?

• A. If an object receives an impulse its kinetic energy must change.
• B. An object's kinetic energy can change without the object changing momentum.
• C. An object can receive a net impulse without any work being done on it.
• D. A force may do work on an object without delivering any change in momentum.

Answer 1

Answer: (A), (B), (D)

An object's kinetic energy can change without the object changing momentum.
If an object receives an impulse its kinetic energy must change.
A force may do work on an object without delivering any change in momentum.

(A) For head on elastic collision of sphere with wall, K.E. of sphere does not change but the sphere receives an impulse. Hence false.
(B) If K.E. of a sphere changes its velocity and thus momentum must change. Hence false.
(C) A force acting perpendicular to velocity changes momentum, but does no work. Hence true.
(D) When a force does work, kinetic energy of body changes. If K.E. changes, velocity and thus momentum must change. Hence false.