A boy standing at the top of a tower of 20m of height drops a stone. Assuming `g=10ms^(-2)`, the velocity with which it hits the ground is :-

Options

A. 10.0 m/s
B. 20.0 m/s
C. 40.0 m/s
D. 5.0 m/s

Answer

B

Explanation

Here , `u = 0 , g = 10 ms^(-2), h = 20 m`
Let v be the velocity with which the stone hits the ground .
`:.v^(2) =u^(2) +2gh`
or `v=sqrt(2gh) = sqrt(2xx 10 xx 20) = 20 m/s ( :. u =0)`