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NTA Abhyas JEE Main2020PhysicsCenter of Mass, Momentum and CollisionPractice

Two massless string of length 5 m hang from the ceiling very near to each other as shown in the figure. Two balls A and B of masses 0 . 25 kg and 0 . 5 kg are attached to the string. The ball A is released from rest at a height of 0 . 45 m as shown in the figure. The collision between two balls is completely elastic. Immediately after the collision, the kinetic energy of the ball B is 1 J . The velocity of ball A jus

Options

  1. A5   m   s - 1 to the right
  2. B5 m s - 1 to the left
  3. C1   m   s - 1 to the right
  4. D1 m s - 1 to the left

Correct answer

D. 1 m s - 1 to the left

Step-by-step solution

KE B = 1 2 m B v B 2 1 = 1 2 × 0 . 5 × v B 2 v B =   2   m   s - 1 u A = 2 gh = 2 × 1 0 × 0 . 4 5 =   3   m   s - 1 From the conservation of linear momentum 0 . 2 5 × 3 + 0 = 0 . 2 5 × v A + 0 . 5 × 2 0 . 7 5 = 0 . 2 5 v A + 1 0 . 2 5 v A = - 0 . 2 5 v A = - 1  m s - 1

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