A mechanic is examining the wheel of a bicycle to adjust the brake. With the bic

Question

A mechanic is examining the wheel of a bicycle to adjust the brake. With the bicycle off the ground, he manually rotates the wheel until it reaches an angular speed of 12.0 rad/s and then allows it to coast to a stop. If the wheel has a moment of inertia of 0.100 kg*m^2, and the wheel slows to a stop in 160 s, what is the magnitude of the retarding torque?

a) 1.00 Nm

b) 0.00750 Nm (<-- correct answer)

c) 0.0787 Nm

d) 1.33 Nm

e) 1.67 Nm

I don't understand which formula(s) I'm supposed to use :(

Explanation / Answer

The relation between torque and angular acceleration is                = I Here = ( - o)/t              = (0 - 12.0 rad/s)/(160 s)              = -0.075 rad/s2 Moment of inertia is I = 0.100 kg .m^2      So the magnitude of retarding torque is                 = (0.100 kg.m2)(0.075 rad/s2)                    = 0.00750 N.m

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