A 715 gram grinding wheel 29.5 {\rm cm} in diameter is in the shape of a uniform solid disk. (We can ignore the small hole at the center.) When it is in use, it turns at a constant 210 {\rm rpm} about an axle perpendicular to its face through its center. When the power switch is turned off, you observe that the wheel stops in 46.5 {\rm s} with constant angular acceleration due to friction at the axle.
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