PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two smooth identical balls A and B, each of mass m, move along the same straight line but in opposite directions with speeds 6.0ms−1 and 4.0ms−1 respectively. They collide perfectly elastically.
(i) Determine the velocities of the two balls immediately after the collision in the laboratory frame.
(ii) Calculate the velocity of the centre of mass of the system and rewrite the initial velocities of the balls with respect to this centre-of-mass frame.
(iii) Show that the magnitudes of the velocities of both balls remain unchanged in the centre-of-mass frame after the collision, and hence comment on the nature of an elastic collision viewed from that frame.