A flywheel is used for the storage of energy in the form of kinetic energy. The

Question

A flywheel is used for the storage of energy in the form of kinetic energy. The flywheel is constructed of a Keviar-epoxy composite with a density of 1,400 kg/m3, allowing the flywheel rim to achieve a safe tangential rim speed of V, = 1,200 m/s at 38,000 RPM. Effectively all the mass of the flywheel, 100 kg, is concentrated at the rim. If energy is removed by connecting the flywheel to an ideal electric generator, how much electric can be generated in bringing the flywheel to rest? What is the specific energy that can be stored in the flywheel, in kilojoules per kilogram, at 38,000 RPM? What is the radius of the flywheel? Ans.72 MJ, 720 kj/kg. 0.302 m

Explanation / Answer

v = 1200 m/s, = 38000 rpm = 38000*2/60 rad/s, m = 100 kg

energy E = mv2/2 = 72 MJ

specific energy = E/m = 720 kJ/kg

radius = v/ = 0.302 m

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