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 244-mile trip in a typical midsize car produces about 4.13 x 109 J of energy. How fast would a 30.1-kg flywheel with a radius of 0.426 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

given

KE = 4.13 X 109 J

m = 30.1 kg , r = 0.426 m ,

I = 0.5 m r2

KE = 0.5 I w2

w = ( 2 KE / I )1/2

w = ( 4 KE / m r2 )1/2  

w = ( 4 X 4.13 X 109 / 30.1 X 0.4262 )1/2

w = 54993.6 rad/sec

w = 525416.56 rev/min

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