Four identical balls `A,B, C` and `D` are placed in a line on frictionless horizontal surface. `A` and `D` are moed with the same speed `u` towards the middle as shown. Assuming elastic collisions, find the final velocities.

Explanation

A and D collides elastically with B and C respectively and come to rest but B and C starts moving with velocity u towards each other as shown

B and C collides elastically and exchange their velocities to move in opposite directions

Now, B and C collides elastically with A and D respectively and come to rest but A and D starts moving with velocity u away from each other as shown

`therefore ` Final velocities `V_(A)=u(larr), V_(B)=0, V_(C)=0`
and `V_(D)=u (rarr)`