Question

A very large number of balls are thrown vertically upwards in quick succession in such a way that the next ball is thrown when the previous one is at the maximum height. If the maximum height is 5m, the number of ball thrown per minute is (take $g = 10ms^{- 2}$)

• A. 120
• B. 80
• C. 60
• D. 40

Answer 1

Answer: (C)

60

Answer 2

Maximum height of ball = 5m, So velocity of projection

$\Rightarrow u = \sqrt{2gh} = \sqrt{2 \times 10 \times 5} = 10m/s$

time interval between two balls (time of ascent)

= $\frac{u}{g} = 1sec = \frac{1}{60}min.$

So no. of ball thrown per min = 60