Two cars collide head-on on a level friction-free road. The collision was completely inelastic and both cars quickly came to rest during the collision. What is true about the velocity of this system's center of mass?
A) It was never zero.
B) It was not initially zero, but ended up zero.
C) It was always zero.

Question

Quizplus · Accepted Answer

In a completely inelastic collision on a frictionless surface, the velocity of the system's center of mass remains constant because of the conservation of momentum. If both cars came to rest together, it implies they had equal and opposite momenta, making the center of mass's velocity zero throughout the event.

Two Cars Collide Head-On on a Level Friction-Free Road