A 45 cm -diameter potter\'s wheel with a mass of 15 kg is spinning at 180 rpm. U

Question

A 45 cm -diameter potter's wheel with a mass of 15 kg is spinning at 180 rpm. Using her hands, a potter forms a 14 cm-diameter pot that is centered on and attached to the wheel. The pot's mass is negligible compared to that of the wheel. As the pot spins, the potter's hands apply a net frictional force of 1.3 N to the edge of the pot. If the power goes out, so that the wheel's motor no longer provides any torque, how long will it take the wheel to come to a stop? You can assume that the wheel rotates on frictionless bearings and that the potter keeps her hands on the pot as it slows. Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

angular velocity = w = 2 pi n/60 = 2 pi (180)/60 = 18.84 rad/sec
I = 1/2 m R^2 = 1/2 (15) (0.225)^2 =0.3796875 N-m sec^2
T = I (Alpha)

1.3 (0.07) = 0.38 (Alpha)

Alpha = 0.2394 rad/sec^2
W f = Wo - (alpha) . t

0 = 18.84 - 0.2394 . t

t= 78.68 sec

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