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 380-mile trip in a typical midsize car produces about 1.30 109 J of energy. How fast would a 16-kg flywheel with a radius of 0.25 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

Rotational KE = .5Iw2

I for a disk is .5mr2, so ...

(1.3 X 109) = .5(.5)(16)(.25)2(w)2

w = 72111 rad/s

Convert to rev/min

72111 X 60/(2pi)

6.89 X 105 rev/min

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