A man throws balls with the same speed vertically upwards one after the other at an interval of 2s. What should be the speed of the throw so that more than two balls are in the sky at any time ? (Given `g = 9.8 m//s^(2)`)

Options

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

Answer

d

Explanation

Ball takes time from initial point to final point where velocity is zero `t=(u)/(g)` and come back at its initial point in same time, total time is 2t, given condition, at least two balls must be in air.
So, `2tgt4` seconds
`(2u)/(g)gt4`
`ugt19.6m//s`