Hello,

We know the time it takes for the ball to reach the ground, ie., 2s.

Now since we're just dropping the ball freely, we assume only gravity to be acting on the body, ie., g=10m/s^2.

Initial velocity u=0.

Final velocity v=x (say).

Using v-u=gt

t=(v-u)/g

Substituting

2=x/10

x=20ms^-1.

Now, distance (height s) = (1/2)*gt^2

= 1/2*10*4

=20m.

Hope it helps!