2008: Problem 14

Topic: System of Masses
Concepts: Conservation of angular momentum, Kinetic energy

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Solution:

Since there are no external torques on the system, we have conservation of angular momentum $L$. Initially, the device has rotational kinetic energy

$$E=\frac{1}{2}I\omega^2=\frac{1}{2}L\omega$$

If the angular velocity is doubled, then the energy is also doubled,

$$E’=2E$$

so the answer is B.

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