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KVPY2015PhysicsMotion in Two Dimensions

A boy is standing on top of a tower of height 85 ~m and throws a ball in the vertically upward direction with a certain speed. If 5.25 seconds later he hears the ball hitting the ground, then the speed with which the boy threw the ball is (take g=10 ~m / s ² , speed of sound in air =340 ~m / s )

Options

  1. A6 ~m / s
  2. B8 ~m / s
  3. C10 ~m / s
  4. D12 ~m / s

Correct answer

B. 8 ~m / s

Step-by-step solution

Time taken by sound = 85 340 =0.25 sec Time taken by the ball =5.25-0.25=5 sec . Now array l -85=u 5- 1 2 10 25 U =8 ~m / sec array

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