A small ball is given some velocity at point A towards right so that it moves on the semicircular track and does not leave contact up to the highest point B. After leaving the highest point B, it falls at the top of a building of height R and width `x(xlt lt 2R)`. (All the surfaces are frictionless).

If the collision of ball with the building is elastic, then the angle with the horizontal at which the ball will rebound from the top of the building is

Options

A. (a) `60^@`
B. (b) `45^@`
C. (c) `30^@`
D. (d) None

Answer

B

Explanation

`v_y=g t`
`v_y=gsqrt((2R)/(g))=sqrt(2gR)`, `v_x=sqrt(2gR)`
`tan theta=v_y/v_x=1`
`theta=45^@`