Question

A child sits stationary at one end of a long trolley moving uniformly with a speed V on a smooth horizontal floor. If the child gets up and runs about on the trolley in any manner, what is the speed of the CM of the (trolley + child) system?

Answer 1

Hey mate,

● Answer-
Velocity of centre of mass remains unchanged

● Explaination-
- Here, the boy running on the trolley (either forward or backward) will exert only internal force on the running trolley.
- Only external forces can affect the centre motion of the body.
- Thus, internal force here will produce no change in velocity of center of mass of the trolley-child system.


Hope that's useful...

Answer 2

Answer:

The child is running arbitrarily on a trolley moving with velocityv. However, the running of the child will produce no effect on the velocity of the centre of mass of the trolley. This is because the force due to the boy’s motion is purely internal. Internal forces produce no effect on the motion of the bodies on which they act. Since no external force is involved in the boy–trolley system, the boy’s motion will produce no change in the velocity of the centre of mass of the trolley.