A stone is projected from the top of a tower with velocity 20ms^–1 making an angle 30º with the horizontal. If the total time of flight is 5s and g = 10ms^–2,

The vertical displaced in 5seconds is given by the equation

$\begin{array}{l}-\mathrm{h}=\mathrm{usin}\mathrm{\theta t}-\frac{1}{2}{\mathrm{gt}}^2\\ \Rightarrow \mathrm{h}=-20\times \frac{1}{2}\left(5\right)+\frac{1}{2}\left(10\right)(5{)}^2\end{array}$
h = -50 + 125 =75m
Height from point of projection
$=\frac{{\mathrm{u}}^2{\sin }^2\mathrm{\theta }}{2\mathrm{g}}=\frac{(20{)}^2{\left(\frac{1}{2}\right)}^2}{\left(2\right)\left(10\right)}=\frac{100}{20}=5\mathrm{m}$
Total height from ground = 75 + 5 = 80m