A heavy ball of mass `2M` moving with a velocity `v_(0)` collides elastically head on with a cradle of three identical ball each of mass `M` as shown in figure. Determine the velocity of each ball after collision.

Explanation

Assume some spacing between the balls

After collision of `2M` with ball 1

`u=((2M-M)/(2M+M))v_(0)=(v_(0))/3, v_(1)=(2(2M)v_(0))/(2M+M)=4/3v_(0)`
Now ball 1 colldes with 2 and itself comes to rest, then 2 will collide with 3 itself comes to rest, so we have

Now again `2M` will collide with ball 1, after this collision we have

Now 1 will collide with 2 and itself comes to rest so we have

Now `2M` will again collide with 1, after this collision we have

So final velocities are as shown in above figure.