Question

A ball is thrown vertically upwards from the top of a tower with an initial velocity $19.6m{s}^{-1}$. The ball reaches the ground after $5s$. Calculate the velocity of the ball on reaching the ground. Take $g=9.8m{s}^{-2}$.

Answer 1

Let us consider point of projection as reference point.
Given, initial velocity, $u=19.6m{s}^{-1}$
Time $\left(t\right)=5s,a=-g=-9.8m{s}^{-2}$,
To find, $v=?$
Using the relation,
$v=u+at$
$v=19.6+(-9.8)\times \left(5\right)$
$v=19.6-49$
$v=-29.4m{s}^{-1}$
$-ve$ sign shows that velocity is in downward direction.
Hence, the velocity of the ball on reaching the ground is $29.4m{s}^{-1}$.