A stone is thrown vertically upwards with an initial speed `u` from the top of a tower, reaches the ground with a speed `3 u`. The height of the tower is :

Options

A. `(3u^(2))/(g)`
B. `(4u^(2))/(g)`
C. `(6u^(2))/(g)`
D. `(9mu^(2))/(g)`

Answer

B

Explanation

`v^(2)=u^(2)+2gh`
`h=(v^(2)-u^(2))/(2g)=(9u^(2)-u^(2))/(2g)=(4u^(2))/(g)`