A body is projected vertically up with velocity u from a tower. It reaches the ground with velocity nu. The height of the tower is `H=u^2/(2g)(n^2-1)`

Explanation

`v^2-u^2=2as`
Here u=u, v=nu , a=-g, s=-H
`(n u)^2-u^2=2gH , (n^2-1)u^2=2gH`
`therefore H=u^2/(2g)(n^2-1)`