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 384-mile trip in a typical midsize car produces about 2.75 x 109 J of energy. How fast would a 12.7-kg flywheel with a radius of 0.259 m have to rotate to store this much energy? Give your answer in rev/min.

Explanation / Answer

Moment of Inertia of flywheel = 0.5 MR2 = 0.5 x 12.7 x 0.2592 = 0.42596435 kgm2

Kinetic Energy of a rotating wheel = 0.5 I2   where is the angular velocity

If KE should be equal to 2.75 x 109 J

2.75 x109 = 0.5 x I2

2.75 x 109  = 0.5 x 0.42596435 x 2

2 = 1.291187866 x 1010

= 113630.4478 rad/ sec

= 113630.4478 x 60 /2 = 1085090.847 rev/ min

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