Question

A stone projected at an angle of $60^\circ $ from the ground level strikes at an angle of $30^\circ $ on the roof of a building of height $h$ . Find the speed of projection of the stone in $ms^{- 1}$ . Take $h=30m,g=10ms^{- 2}$

Answer 1

Let initial and final speed of stone be $u$ and $v.$
$\therefore v^{2}=u^{2}-2gh$
And $vcos30^\circ =ucos60^\circ $
Solving above equations we get
$u=\sqrt{3 g h}$