The ball `A` is reached and it makes head on collision with `B`. The masses of `A` and `B` are same

Options

A. After collision , `A` comes to rest and `B` moves with velocity of `A` just before collision
B. The maximum height attained by ball `B is L//2`
C. The maximum angle made by string attached to `B is 60^(@)`
D. All options are correct

Answer

D

Explanation

When ball `A` collides with `B` , speed of `A`
`u_(1)^(2) = 0 + 2g (L)/(2) rArr u_(1) = sqrt(gL)`
After the elastic collision (head - on) , velocities of balls are exchanged , `(1)` is `O.K.`
`h = (L)/(2), (2) is O.K`.
`h = L(1 - cos theta) rArr (L)/(2) ,(L)/(2) = L(1 - cos theta)`
`rArr theta = 60^(@) ,(3) is O.K`.