A flywheel is a solid disk that rotates about an axis that is perpendicular to t

Question

A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a possible alternative to batteries in electric cars. The gasoline burned in a 260 mile trip in a typical midsize car produces about 1.50 109 J of energy. How fast would a 16 kg flywheel with a radius of 0.29 m have to rotate in order to store this much energy? Give your answer in rev/min.

_______rev/min

Explanation / Answer

The energy of a rotatng flywheel is found by

KE = .5I2

I for a flywheel (disc) is .5MR2 = (.5)(16)(.29)2 = .6728 kgm2

So, by substitution

(1.5 X 109) = (.5)(.6728)(2)

= 66776 rad/s

Since there are 2 rad/rev, and 60 sec in a minute, 66766 rad/s = 6.38 X 105 rev/min

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