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 350-mile trip in a typical midsize car produces about 4.27 x 109 J of energy. How fast would a 6.70-kg flywheel with a radius of 0.402 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

Moment of inertia of flywheel

I=(1/2)mR2=(1/2)*6.7*0.4022=0.54 kg-m2

Kinetic energy

K=(1/2)IW2

4.27*109=(1/2)*0.54*W2

W=1.256*105 rad/sec

in rev/min

1 rad/sec =(60/2pi) rev/min

W=1.256*105*60/2pi

W=1.2*106rev/min

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