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NEET PHYSICSMOTION IN A PLANEMedium

Question

A man throws balls with the same speed vertically upwards one after the other at an interval of 2 seconds2 \text{ 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/s2g=9.8 \text{ m/s}^2)

A

At least 0.8 m/s0.8 \text{ m/s}

B

Any speed less than 19.6 m/s19.6 \text{ m/s}

C

Only with speed 19.6 m/s19.6 \text{ m/s}

D

More than 19.6 m/s19.6 \text{ m/s}

Step-by-Step Solution

  1. Analyze the Condition: The problem states that balls are thrown at intervals of Δt=2 s\Delta t = 2 \text{ s}. For 'more than two balls' (i.e., at least 3) to be in the sky simultaneously, the first ball must remain in the air until the third ball is thrown.
  2. Time Constraint: Let the time of flight for a single ball be TT. If the third ball is thrown at t=2Δt=4 st = 2\Delta t = 4 \text{ s}, the first ball (thrown at t=0t=0) must not have landed yet. Therefore, the time of flight must be greater than 4 s4 \text{ s} (T>4 sT > 4 \text{ s}).
  3. Formula for Time of Flight: For an object thrown vertically upwards with speed uu and returning to the same level, the total time of flight is given by T=2ugT = \frac{2u}{g} .
  4. Calculation: 2ug>4\frac{2u}{g} > 4 2u>4g2u > 4g u>2gu > 2g Substitute g=9.8 m/s2g = 9.8 \text{ m/s}^2: u>2×9.8u > 2 \times 9.8 u>19.6 m/su > 19.6 \text{ m/s}
  5. Conclusion: The speed of the throw must be more than 19.6 m/s19.6 \text{ m/s}.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from MOTION IN A PLANE. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSMOTION IN A PLANEthrowsverticallyupwardsintervalseconds

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