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

Multiple Choice

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 always zero.
B) It was never zero.
C) It was not zero, but ended up zero.
D) none of the above