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COMEDK2015PhysicsMotion in One Dimension

A ball is dropped from the top of the building 100 ~m high. Simultaneously, another ball is thrown upwards from the bottom of the building with such a velocity that the balls collide exactly mid-way. What is the speed in ms ⁻¹ with which the second ball is thrown? (Take, g=10 ~ms ⁻² )

Options

  1. A31.6
  2. B27.8
  3. C22.4
  4. D19.6

Correct answer

A. 31.6

Step-by-step solution

The given situation is shown in the figure. For the first ball, time taken to reach at mid point A , aligned t &= 2 h g &= 2 50 10 = 10 ~s aligned For the second ball, aligned v &=0, u=?, a=-g From equation, v &=u+g t 0 &=u-g t₁ t₁ &= u g aligned Since, both balls collide at some time, Hence, aligned t &=t₁ 10 &= u g u &=10 10 ~m / s =31.6 ~m / s aligned

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