A stone dropped from the top of a tower touches ground in 4 seconds. The height of the tower is $\left(\mathrm{g}=10{\mathrm{ms}}^{-2}\right)$

Initial velocity u = 0, time t = 4 s

$\text{ Acceleration }\mathrm{a}=g=10{\mathrm{ms}}^{-2}\Rightarrow \text{ Height of the tower }\mathrm{h}=\text{ ? }$

$\mathrm{S}=\mathrm{ut}+\frac{1}{2}{\mathrm{at}}^2\Rightarrow h=0+\frac{1}{2}\left(10\right)(4{)}^2\Rightarrow \mathrm{h}=80\mathrm{m}$