Question

An 80 lb wheel of 2 ft radius of gyration is rotating at 360 rev/min. If the retarding frictional torque is 4 lb-ft, calculate the time it will take the wheel to coast to rest.

Answer 1

Answer:

m = 80 lb

k = 2 ft

We know k = $\sqrt{I/m}$

So 2 = √(I/80)

I = 320 lb ft²

ω = 360 rpm = (360 x 2π/60) = 120π rad/sec

Now, resulting rotational torque τ = I α

τ = 320 x (120π/t)

For the wheel to come to rest, net torque must be zero.

Therefore rotational torque must be equal to frictional torque.

320 x (120π/t) = 4

t = 9600π sec

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