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 197-mile trip in a typical midsize car produces about 2.41 x 109 J of energy. How fast would a 40.3-kg flywheel with a radius of 0.303 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

Given

KE = 2.41*10^9 J

m = 40.3 kg

R = 0.303 m

let w is the nagular speed of the fly wheel to store the given amount of energy.

Apply, KE = (1/2)*I*w^2 (here I is moment of inertia of flywheel)

==> w = sqrt(2*KE/I)

= sqrt(2*KE/(0.5*M*R^2))

= sqrt(4*KE/(M*R^2))

= sqrt(4*2.41*10^9/(40.3*0.303^2))

= 51044 rad/s

= 51044*60/(2*pi)

= 4.87*10^5 rev/min

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