A man throws balls with the same speed vertically upwards one after the other at an interval of 2 second. What should be the speed of the throw so that two balls are in the sky at any time?

Options

A. At least 9.8 `m//s`
B. Any speed less than `19.6m//s`
C. Only with speed `19.6 m//s`
D. More than `19.6 m//s`

Answer

d

Explanation

For more than 2 balls to be in the air, the time interval should be t>(2+2)s or 4 s.
The maximum time of flight for each ball is `=(2u)/(g)`
Thus `(2u)/(g)` >4 s or u > 2g
Bur g=9.8 `ms^(-2)`
`:. ` u> 19.6 `ms^(-1)`