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//s` in a direction making `60^(@)` with the line of centres at the time of impact.
A. The sphere A comes to rest after collision.
B. The sphere B will move with a speed of `8 m//s` after collision
C. The directions of motion A and B after collision are at right angles.
D. The speed of B after collision is `4 m//s`

Answer 1

Correct Answer - C::D
Component of velocity of A along common normal is `v cos 60^(@)` and this velocity of A after collision with B is interchanged. Hence A moves along `v sin 60^(@)` which is normal to common normal.