Question

A boy throws a rubber ball vertically downwards
He wants the ball to rebound from the floor and
touch the ceiling of the room which is at a height of
5 m. The coefficient of restitution is 0.9. With what
velocity should the ball strike the floor ?​

Answer 1

Thus the ball strike the floor with velocity V = 8.94 m/s

Explanation:

As we know that

coefficient of restitution, e = √ h′ / h

(e)^2 = h' / h

(0.9)^2 = h' / 5

0.81 x 5 = h'

h' = 4 m

Now

We know that

P.E = K.E

mgh = 1/2 mv^2

gh' = 1/2 V^2

v^2 =   2gh'

V = √2gh' =  √ 2 x 10 x 4 = √ 80

V  = 8.94 m/s

Thus the ball strike the floor with velocity V = 8.94 m/s