A ball A is thrown up vertically with a speed u and at the same instant another ball B is released from a height h, At time t, the speed of A relative to B is

Options

A. a)u
B. b)2u
C. c)`u-gt`
D. d)`sqrt((u^2 -gt))`

Answer

A

Explanation

From equation of motion, we have
`v=u+g t`
where u is initial velocity and t is time
For ball A, `v_A=u- g t`
For ball B, `v_B=0+ g t`
`therefore` Relative speed , `Delta vec v= vec v_A-vecv_B`
`(u- g t) hat j- (- g t hatj)`
`=u hat j`