Balls are thrown vertically upwards in such a way that the next ball is thorwn when the previous one is at the maximum height. If the maximum hieght is `5m`, the number of balls thrown per minute will be

Options

A. 120
B. 80
C. 60
D. 40

Answer

C

Explanation

Given that maximum height = 5 m , g = `10 ms ^(-2)`
Now , `v^2 =u^2 -2gs`
or ` 0 = u^(2) -2 xx 10 xx 5 =u^(2) - 100 " or " u^(2) = 100`
`:. u = 10 ms ^(-1)`
Further , at maximum height , v = 0
`:. 0 = u - gt = 10 - 10 xx t " or " t = 1 s `
It means that each ball is thrown after 1 s. Therefore , number of balls thrown per minute = 60 .