flywheel is a solid disk that rotates about an axis that is perpendicular to the

Question

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 210 mile trip in a typical midsize car produces about 1.60 109 J of energy. How fast would a 16 kg flywheel with a radius of 0.34 m have to rotate in order to store this much energy? Give your answer in rev/min.

Explanation / Answer

The energy should be stored E = 1.6*10^9 J

the mass of the wheel M = 16kg

the radius of the wheel R = 0.34m

Then the energy stored in the wheel

               K = 1/2 I^2

Here the moment of inertia I = 1/2MR^2

                                               = (0.5)(16)(0.34)^2

                                                = 0.9248 kgm^2

therefore the angular speed

                   = 2K/I

                      = 2(1.6*10^9)/0.9248

                     =5.88*10^4 rad/s

                     = 56.2 rev/min

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