(b) When two bodies of equal masses colides elastically their velocities are interchanges. When ball 1 collides with ball-2 then velocity of ball-1. `v_(1)` becomes zero and velocity of ball-2, `v_(2)` becomes v,i.e. similarity
When ball 2 collides will ball 3
`{:(,v_(1)=0,Rightarrow v_(2)=v),(,v_(2)=0,v_(3)=v):}`