A car is designed to get its energy from a rotating flywheel with a radius of 2.

Question

A car is designed to get its energy from a rotating flywheel with a radius of 2.25 m and a mass of 525 kg. The flywheel can be considered as a uniform thin cylinder. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 5000 rev/min.
a)What is the kinetic energy stored in the flywheel?
b)If the flywheel is to supply energy to the car as would a 20-hp motor, find the length of time the car could run before the flywheel would have to be brought back up to speed.

Explanation / Answer

a)KE=0.5I2=0.25MR22=1.82*108J

b)Time=KE/power=1.82*108J/746*20=12209s=3.39 hours

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