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Question: Answered & Verified by Expert
A child is standing at one end of a long trolley moving with a speed v on a smooth horizontal track. If the child starts running towards the other end of the trolley with a speed u , the centre of mass of the system (trolley + child) will move with a speed
PhysicsCenter of Mass Momentum and CollisionNEET
Options:
  • A zero
  • B v+u
  • C v-u
  • D v
Solution:
1220 Upvotes Verified Answer
The correct answer is: v
Internal forces can not change the velocity of the center of mass of the system. Therefore it continues to move with the same speed.

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