2011: Problem 24

Topic: Rigid Bodies
Concepts: Power, Torque

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Solution:

The power supplied is given by

$$P=\tau\omega$$

where $\tau$ is the torque supplied to the ring and $\omega$ is the rotation rate. The torque supplied to the ring has to balance the torque from friction so

$$\tau=fR=\mu NR$$

$$P=\mu NR\omega$$

Increasing $R$ increases the power required while increasing $\delta$ has no effect at our level of approximation so the answer is A.

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