A ball is thrown vertically upwards from a height of 40 m and hits the ground with a speed that is three times its initial seepd. What is the time taken (in sec) for the fall ?

Answer

4

Explanation

`9v^(2)=v^(2)+2xx10x40`
`v^(2)=100, u=10 m//s`
`s/t=(v+u)/2`
`rArr (-40)/t= (10-30)/2=-10`
`t=4 sec`