Two children, each with mass m=18.5kg, sit on opposite ends of a narrow board wi

Question

Two children, each with mass m=18.5kg, sit on opposite ends of a narrow board with length L=5.8m, width W=0.21m, and mass M=6.0kg. The board is pivoted at its center and is free to rotate in a horizontal circle without friction.

While the system is rotating, the children pull themselves toward the center of the board until they are half as far from the center as before What is the resulting angular speed?

What is the change in kinetic energy of the system as a result of the children changing their positions?

Explanation / Answer

conserving angular momentum

2m x L/2 x = 2m x L/4 x '

or ' = 2

and since there is no externel effect kinetic energy will remain same as before

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