The greatest fluctuation of energy to be stored by an engine flywheel is 2kJ when the mean engine speed is 4 rev/s. The speed variation is to be limited to ?1% and the mass of the flywheel is 450kg. The flywheel is a cast iron ring with an internal diameter = 0.9 of the external diameter. Find the diameters and the thickness of the ring given ?cast iron = 7.2Mg/m^3