A ball is gently dropped from a height of $20m$. If its velocity increases uniformly at the rate of $10{ms}^{-2}$, with what velocity will it strike the ground? After what time will it strike the ground?

Height, $s=20m$

Acceleartion , $a=10m/s^2$

By 3rd equation of motion

$v^2=u^2+2as$

$v^2=0+2\times 10\times 20=400$

$\Rightarrow v=20m/s$

So, we conclude final velocity , $v=20m/s$

again, by 1st equation of motion , $v=u+at$

$\Rightarrow t=\frac{v-u}{a}$

$\Rightarrow t=\frac{20}{10}=2s$

So, it will strike the ground after $2s$