Question

A smooth sphere A of mass m collides elastically with an identical sphere B at rest. The velocity of A before collision is 8 m/* in a direction making 60 with the line joining the centres at the time of impact. Which of the following is/are possible :

(A) the sphere A comes to rest after collision

(B) the sphere B will move with a speed of 8 m/ after collision

(C) the directions of motion of A and B after collision are at right angles

(D) the speed of B after collision is 4 m/*.

Answer 1

Correct option (C,D)

Explanation:

Sphere A moving with velocity v has a component v/2 along the line joining the centres of the spheres at the time of collision and another component v/2 perpendicular to the previous direction. After collision the component along the line will interchange i.e. B will move with v/2 velocity i.e. 4 m/* along the line joining the centres and A moves with v/2 velocity at perpendicular direction to B.