A perfectly elastic ball P1 of mass m moving with velocity v collides elastically with three exactly similar balls P2, P3, P4 lying on a smooth table as shown. Velocities of the four balls after the collision are

In perfect elastic collision b/w bodies of equal masses they exchange their velocities.After collision between P1 and P2 , p1 comes to rest and P2 starts moving with velocity V .For collision between P2 and P3 , P2 comes to rest and P3 starts moving with velocity V .Finally , for collision between P3 and P4 , P3 comes to rest and P4 starts moving with velocity V.