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 258-mile trip in a typical midsize car produces about 1.94 x 109 J of energy. How fast would a 22.1-kg flywheel with a radius of 0.495 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

moment of inertia of flywheel is

KE = ( 1/ 2) I w ^2

= ( 1/ 4) M r ^2 w ^2

w ^2 = 4 K E / M r ^2

w = sqrt ( 4 (1.94*10^ 9 J ) / (22.1 kg ) (0.495 m )^2 )

= 37855.54 rad /s

= 361493 rev/min

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