A stone is thrown upwards with initial velocity 'u' from top of a tower and it reaches to ground with velocity '3u' then height of the tower is ......

Options

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

Answer

B

Explanation

`(3u) ^(2) -u^(2) =2gh`
`(because v = 3u, u=u, a = g and x=h)`
`therefore 9u^(2) -u^(2) =2gh`
`therefore h = (8u^(2))4u^(2))/(g)`