Answer :

When the ball reaches the highest point, its velocity will be zero. So final velocity is :

v=0m/s

Here, the time to reach highest point is equal to time to hit ground from highest point.

Consider upward motion, the acceleration of the ball is

a=−g=−9.8m/s2

(minus for motion opposite to gravity)

If It be the required time.

Using

v=u+at,0=25+(−9.8)t⟹ t=2.5s

Thus the ball hits the ground after

2.5

seconds after reaching its highest point.