it has been suggested that we should use our power plants to generate energy in the off-hours (such as late at night) and store it for use during the day. one idea put forward is to store the energy in large flywheels. suppose we want to build such a flywheel in the shape of a hollow cylinder of inner radius 0.5 m and outer radius 1.5 m , using concrete of density 2200 kg/m^3. if, for stability, such a heavy flywheel is limited to 1.75 seconds for each revolution and has negligible friction at its axle, what must be its length to store 2.5 mj of energy in its rotational motion?
