Using the equations of motion;

`darr V^2 = U^2+2*a*S `

`V = 7.5` `m/s`

`U = ?`

`a = g = 10` `m/s^2`

`S = 2m`

`U = sqrt(V^2-2*a*S)`

`U = sqrt(7.5^2-2*9.81*2)`

`U = 4.124m/s`

*So the initial speed of the ball is 4.124m/s*

Using the equations of motion;

`darr V^2 = U^2+2*a*S `

`V = 7.5` `m/s`

`U = ?`

`a = g = 10` `m/s^2`

`S = 2m`

`U = sqrt(V^2-2*a*S)`

`U = sqrt(7.5^2-2*9.81*2)`

`U = 4.124m/s`

*So the initial speed of the ball is 4.124m/s*