$9\mathrm{.}42.$ You need to design an industrial turntable that is $60\mathrm{.}0$ cm in diameter and has a kinetic energy of $0\mathrm{.}250$ J when turning at $\backslash (45\mathrm{.}0\backslash$mathrm$\{$rpm$\}(\backslash$mathrm$\{$rev$\}/\backslash$mathrm$\{$min$\})\backslash ).($a$)$ What must be the moment of inertia of the turntable about the rotation axis? $($b$)$ If your workshop makes this turntable in the shape of a uniform solid disk, what must be its mass?