Two objects undergo a collision, and there is no external force on the objects. Which of the following must be true?
A) Both objects move at constant velocity.
B) The objects have equal and opposite velocities.
C) The center of mass moves with constant velocity.
D) The center of mass is stationary.

Question

Quizplus · Accepted Answer

If there is no external force on the objects, then the total momentum of the system (the two objects) is conserved. This means that if one object gains a certain amount of momentum, the other must lose the same amount of momentum. Therefore, their velocities after the collision will depend on their masses and their initial velocities. However, the center of mass of the system will remain unchanged because there is no external force acting on it. This means that it will continue to move with a constant velocity. Choice A cannot be true because the velocities of the objects may change depending on their masses and initial velocities. Choice B is also untrue because the objects may have different and non-opposite velocities after the collision. Choice D is untrue because the center of mass must move with a constant velocity, but it may not necessarily be stationary.

Two Objects Undergo a Collision, and There Is No External