It has been argued that power plants should make use of off$-$peak hours $($such as late at night$)$ to generate mechanical energy and store it until it is needed during peak load times, such as the middle of the day. One suggestion has been to store the energy in large flywheels spinning on nearly frictionless ball bear$-$ings. Consider a flywheel made of iron $($density $7800$ kg$/$m$?)$ in the shape of a $10\mathrm{.}0-$cm$-$thick uniform disk. $($a$)$ What would the diameter of such a disk need to be if it is to store $10\mathrm{.}0$ megajoules of kinetic energy when spinning at $90\mathrm{.}0$ rpm about an axis perpen$-$dicular to the disk at its center b What would be the centripetalacceleration of a point on its rim when spinning at this rate?