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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/s²)

Asked in NEET 2003 · Successive drops

• (1) more than 19.6 m/s
• (2) at least 9.8 m/s
• (3) any speed less than 19.6 m/s
• (4) only with speed 19.6 m/s

Step-by-step solution

Why the other options are wrong

• (2) A time of flight of 2 s only keeps one ball up at a time: the first lands exactly as the second is thrown.
• (3) Has the inequality backwards. A slower throw means a shorter flight, so fewer balls are in the air at once, not more.
• (4) Exactly 19.6 m/s gives a flight of exactly 4 s, so the third ball is thrown at the instant the first lands. More than two in the air needs a flight longer than 4 s.

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