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 223-mile trip in a typical midsize car produces about 4.88 x 109 J of energy. How fast would a 15.6-kg flywheel with a radius of 0.584 m have to rotate to store this much energy? Give your answer in rev/min. I feel like I have tried every equation possible and cannot seem to get the correct answer. The answer I keep getting is 5708937 and this is incorrect. Someone please help me out. Thanks in advance.

Explanation / Answer

moment of inertia of disk = 0.5 * mass * radius^2

moment of inertia of disk = 0.5 * 15.6 * 0.584^2

moment of inertia of disk = 2.66 kg.m^2

by conseration of energy

initial energy = final energy

4.88 * 10^9 = 0.5 * 2.66 * w^2

angular speed w = 60573.6983 rad/sec or 578436.21 rev/min

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