Two equal masses travel in opposite directions with equal speed.If they collide in a perfectly elastic collision,then,just after the collision,their velocities will be
A)zero.
B)equal to their original velocities.
C)equal in magnitude but opposite in direction to their original velocities.
D)less in magnitude and in the same direction as their original velocities.
E)less in magnitude and opposite in direction to their original velocities.

Question

Quizplus · Accepted Answer

In a perfectly elastic collision, both momentum and kinetic energy are conserved. Since the two masses have equal magnitudes of momentum in opposite directions before the collision, the total momentum of the system is zero. Therefore, the total momentum of the system must be zero after the collision as well, which means that the two masses must have equal magnitudes of momentum in opposite directions after the collision. This corresponds to choice C, where the velocities are equal in magnitude but opposite in direction to their original velocities.

Two Equal Masses Travel in Opposite Directions with Equal Speed