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 370 mile trip in a typical midsize car produces about 1.90 109 J of energy. How fast would a 13 kg flywheel with a radius of 0.25 m have to rotate in order to store this much energy? Give your answer in rev/min.
____ rev/min

Explanation / Answer

E = 1/2 I w^2 where w is the angular frequency w = (2 E / I)^1/2 I = 1/2 M R^2 the moment of inertia w = 2 (E / M)^1/2 / R w = 2 * (1.9 * 10E9 / 13)^1/2 / .25 = 9.67 * 10E4 / sec f = w / (2 * pi) = 9.67 ^ 10E4 / 6.28) = 15,400 rev / sec f = 60 sec/min * 15,400 rev/sec = 9.24 * 10E5 rev/min

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