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 160-mile trip in a typical midsize car produces about 3.35 x 109 J of energy. How fast would a 33.5-kg flywheel with a radius of 0.214 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

Rotational Kinetic energy = 3.35 x 109 J

I = moment of inertia of flywheel = mr2 /2 = (33.5) (0.214)2 /2 = 0.7671 kgm2

let the angular speed = w

Using the formula

(0.5) I w2 = 3.35 x 109

(0.5) (0.7671) w2 = 3.35 x 109

w = 9.35 x 104 rad/s

w = 9.35 x 104 rad/s (60 sec/1 min) (1 rev/6.28 rad)

w = 89.33 x 104 rev/min

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