A passenger bus in Zurich, Switzerland derived its motive power from the energy

Question

A passenger bus in Zurich, Switzerland derived its motive power from the energy stored in a large flywheel. The wheel was brought up to speed periodically, when the bus stopped at a station, by an electric motor, which could then be attached to the electric power lines. The flywheel was a solid cylinder with a mass of 1090kg and a diameter of 1.90m ; its top angular speed was 2950rev/min .

Part A

At this angular speed, what is the kinetic energy of the flywheel?

Part B

If the average power required to operate the bus is 1.85

Explanation / Answer

As

KE = 1/2 I w^2

and

R = 1.90 m/2 = 0.95 m

I = 1/2 M R^2

w = 2950 rpm = 308.92 rad/s

Then

KE = 2.347*10^7 J   [ANSWER]

****************

As

t = KE / P

Then

t = 1270 s   [ANSWER, PART B]

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