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JEE Main 2021 (20 Jul, Shift 2) · Relative Velocity

Relative Velocity question from JEE Main 2021 (20 Jul, Shift 2)

Q7JEE Main 2021 · 20 JUL · SHIFT 2Medium

Relative Velocity

A boy reaches the airport and finds that the escalator is not working. He walks up the stationary escalator in time t1. If he remains stationary on a moving escalator then the escalator takes him up in time t2. The time taken by him to walk up on the moving escalator will be:

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Answer: (c)

  1. Boy's speed Lt1\frac{L}{t_1}, escalator speed Lt2\frac{L}{t_2}; speeds add.
  2. t=LL/t1+L/t2=t1t2t1+t2t = \frac{L}{L/t_1 + L/t_2} = \frac{t_1t_2}{t_1 + t_2}
  3. So the answer is (c).
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