Motion in a Straight Line - Result Question 42
44. A man throws balls with the same speed vertically upwards one after the other at an interval of 2 seconds. What should be the speed of the throw so that more than two balls are in the sky at any time? [Given $g=9.8 m / s^{2}$ ] [2003]
(a) Only with speed $19.6 m / s$
(b) More than $19.6 m / s$
(c) At least $9.8 m / s$
(d) Any speed less than $19.6 m / s$
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Answer:
Correct Answer: 44. (b)
Solution:
- (b) Let the required speed of throw be $u$ $ms^{-1}$. Then time taken to reach maximum height,
$t=\frac{u}{g}$
For two balls to remain in air at any time, $t$ must be greater than 2 .
$ \therefore \quad \frac{u}{g}>2 \Rightarrow u>19.6 m / s $
