45. A flywheel is a solid disk that rotates about an axis that isperpendicular t

Question

45. A flywheel is a solid disk that rotates about an axis that isperpendicular to the disk at its center. Rotating flywheels providea means for storing energy in the form of rotational kinetic energyand are being considered as a possible alternative to batteries inelectric cars. The gasoline burned in a 300-mile trip in a typicalmidsize car produces about 1.2 X 109 J of energy. Howfast would a 13-kg flywheel with a radius of 0.30 m have to rotatein order to store this much energy/ Give your answer inrev/min.

Explanation / Answer

   We know that       KE = 1/2 I2      1.2*109 J = 1/2 (1/2mr2 ) 2    2  =  1.2*109 J/ (1/4 * 13 (0.3)2 ) =4.1*109   therefore =6.4*104 rad/s       = 61*104 rev/min      1.2*109 J = 1/2 (1/2mr2 ) 2    2  =  1.2*109 J/ (1/4 * 13 (0.3)2 ) =4.1*109   therefore =6.4*104 rad/s       = 61*104 rev/min    2  =  1.2*109 J/ (1/4 * 13 (0.3)2 ) =4.1*109   therefore =6.4*104 rad/s       = 61*104 rev/min   therefore =6.4*104 rad/s       = 61*104 rev/min

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