When a ball A is thrown in vertically upward direction with velocity `20 ms^(-1),` exactly at the same time another ball B is allowed to fall freely from height 1. The magnitude of velocity of A with respect to B at time 2 sec is ...... `ms^(-1) (g = 10 m//s^(2)`)

Options

A. 40
B. 10
C. 20
D. 30

Answer

C

Explanation

Velocity of ball A at time t `= v _(A) = v _(0) - g t`
Velocity of ball B at time `t = v _(B) = 0 - g t = g t`
Velocity of ball A w.r.t. is `= v _(A) - g t + g t = v _(0) = 20 ms ^(-1)`