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JEE Main202127 Jul 2021Morning ShiftPhysicsCenter of Mass, Momentum and CollisionActual

Three objects A , B and C are kept in a straight line on a frictionless horizontal surface. The masses of A , B and C are m , 2 m and 2 m respectively. A moves towards B with a speed of 9 m s - 1 and makes an elastic collision with it. Thereafter B makes a completely inelastic collision with C . All motions occur along the same straight line. The final speed of C is :

Options

  1. A6   m   s - 1
  2. B9   m   s - 1
  3. C4   m   s - 1
  4. D3   m   s - 1

Correct answer

D. 3   m   s - 1

Step-by-step solution

Collision between A and B m × 9 = m v 1 + 2   m v 2 (from momentum conservation) e = 1 = v 2 - v 1 9 ⇒ v 2 = 6   m   sec - 1 ,   v 1 = - 3   m   sec - 1 Collision between B and C 2   m × 6 = 4 m v (from momentum conservation) v = 3   m   s - 1

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