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NTA Abhyas JEE Main2020PhysicsCenter of Mass, Momentum and CollisionPractice

Two masses m and M ( > m ) are joined by a light string passing over a smooth light pulley. The centre of mass of the system moves with an acceleration

Options

  1. Ag M - m M + m downward
  2. Bg M - m M + m 2 downward
  3. Cg M - m M + m 2 upward if M < m
  4. Dz e r o

Correct answer

B. g M - m M + m 2 downward

Step-by-step solution

a c o m = m 1 a 1 ¯ + m 2 a 2 ¯ m 1 + m 2 a c o m = 1 m + M [ M ( M − m ) m + M - m ( M − m ) m + M ] g = 1 m + M [ ( M − m ) 2 m + M ] g = ( M − m M + m ) 2 g

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