A ?ywheel in the form of a heavy circular disk of diameter 0.881 m and mass 168

Question

A ?ywheel in the form of a heavy circular
disk of diameter 0.881 m and mass 168 kg is
mounted on a frictionless bearing. A motor
connected to the ?ywheel accelerates it from
rest to 835 rev/min.
What is the moment inertia of the flying wheel?

How much work is done on it during this
acceleration?
Answer in units of J

After 835 rev/min is achieved, the motor is
disengaged. A friction brake is used to slow
the rotational rate to 334 rev/min.

What is the magnitude of the energy dissi-
pated as heat from the friction brake?

Explanation / Answer

Part A)

I = .5mr^2

I = (.5)(168)(.4405)^2

I = 16.3 kg m^2

Part B)
W = change in KE

KE = .5(I)(w^2)

w = 835 rev/min = 87.44 rad/s

W = (.5)(16.3)(87.44)^2

W = 62314 J

Part C)
The Energy at 334 rev/min (34.98 rad/s)

KE = .5(16.3)(34.98)^2 = 9970 J

62314 - 9970 = 52344 J

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