A body is projected vertically upwards with speed u from the top of a tower. It strikes at the ground with speed 3u. What is (a) height of tower and (b) time take by the body to reach at the ground?

Explanation

(a) Let upwards be negative direction.
In vertical direction `v^(2)=u^(2)+2as`
Here `v=3u, u=-u, a=g, s=h`
`9u^(2)=u^(2)+2g(h)rArrh=(8u^(2))/(2g)=(4u^(2))/(g)`
(b) In vertical direction `v=u+atrArr3u=-u+gtrArrt=(4u)/(g)`