The ball is released when the string is horizontal. The collision between the ball and the block is head - on elastic. The velocities of the ball and the block immediately after collision

Options

A. `(2)/(3) sqrt(2 gL) ,(1)/(3) sqrt( 2gL)`
B. `-(2)/(3) sqrt(2 gL) ,(1)/(3) sqrt( 2gL)`
C. `(2)/(3) sqrt(2 gL) , -(1)/(3) sqrt( 2gL)`
D. `-(2)/(3) sqrt(2 gL) , -(1)/(3) sqrt( 2gL)`

Answer

B

Explanation

When the ball reaches to the block , its velocity ` = sqrt(2 gL)`
`m sqrt(2 gL) + 2 m xx 0 = mv_(1) + 2 m v_(2)` (i)
`v_(1) + sqrt(2 gL) = v_(2) + 0` (ii)
Similarly, `v_(1) = -(2)/(3) sqrt(2g L) , v_(2) = (1)/(3) sqrt(2g L)`
That is after collision , the ball moves to the left and the block to the right.