A group of children is riding on a playground merry-go-round. Initially they are

Question

A group of children is riding on a playground merry-go-round. Initially they are all at the perimeter, and a friendly parent gives it a good push to get it rotating, but then sits down with coffee and his smartphone. Then the children all move towards the center. Assume that the merry-go-round has good bearings, so we can neglect any torque due to friction. When the children move from the perimeter to the center:

a) Is angular momentum conserved? Why or why not?

b) Is rotational kinetic energy conserved? Why or why not?

c) Does the angular velocity of the merry-go-round increase, decrease or remain constant? Why?

d) If either angular momentum or rotational kinetic energy (or both) is not conserved, does the quantity increase or decrease when the children move to the center? What accounts for the change?

Explanation / Answer

1) yes , here no external torque acts on the system

2) yes, no conservative forces (friction) are acting

3) increases. because moment of inertia decreases

4) decreases

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