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

Question

A man throws balls with same speed vertically upwards one after the other at an interval of 2 s. What should be the speed of throw so that more than two balls are in the sky at any time ? (A) Only with speed 19.6 ms-1 (B) More than 19.6 ms-1 (C) At least 9.8 ms-1 (D) Any speed less than 19.6 ms-1

Tardigrade Admin · Accepted Answer

Interval of ball thrown = 2 s If we want that minimum three (more than two) balls remain in air then time of flight of first ball must be greater than 4 s. T > 4 s ⇒ (2u/g) > 4s ⇒ u > 19 .6 m s-1

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

Only with speed $19.6 m s^{- 1}$

More than $19.6 m s^{- 1}$

At least $9.8 m s^{- 1}$

Any speed less than $19.6 m s^{- 1}$

Interval of ball thrown $= 2 s$ If we want that minimum three (more than two) balls remain in air then time of flight of first ball must be greater than $4 s$ .
$T > 4 s$
$\Rightarrow \frac{2 u}{g} > 4 s$
$\Rightarrow u > 19.6 m s^{- 1}$

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

Only with speed 19.6ms−1

More than 19.6ms−1

At least 9.8ms−1

Any speed less than 19.6ms−1