A rod rests on frictionless ice. Forces that are equal in magnitude and opposite in direction are simultaneously applied to its ends as shown. The quantity that vanishes is its:
A) angular momentum
B) angular acceleration
C) total linear momentum
D) kinetic energy
E) rotational inertia

Question

A rod rests on frictionless ice. Forces that are equal in magnitude and opposite in direction are simultaneously applied to its ends as shown. The quantity that vanishes is its: 
A) angular momentum 
B) angular acceleration 
C) total linear momentum 
D) kinetic energy 
E) rotational inertia

Quizplus · Accepted Answer

Since the two forces are equal and opposite, there is no net force acting on the rod, so the total linear momentum of the system remains constant. This means that the quantity that vanishes is the change in linear momentum, which is the total impulse applied to the rod. The angular momentum, angular acceleration, kinetic energy, and rotational inertia of the rod are not affected by the external forces, so they do not vanish.

A Rod Rests on Frictionless Ice