Let  the time taken by ball to reach at maximum height  is `t_0`

At maximum height , v = 0

Here                 `h = ((u + v))/(2) t`

or                     `5 = u/2 t_0`

`:.`                    `t_0  = 10/u`

But for upward motion,          `v^2 = u^2 - 2gh`

or                   `(0)^2 = u^2 - 2 xx 10 xx 5`

`:.`             `u^2       = 2 xx 10 xx 5`

                 `u = sqrt(2 xx 10 xx 5)   `  = 10 m/s

`:.`           Number of balls per minute `= t/t_0 = (1min)/(1sec) =( 60sec)/(1sec) = 60 sec`