13. Rotational Inertia & Energy

Which of the following expressions correctly gives the rotational kinetic energy $K$ of a rotating wheel with moment of inertia $I$ and angular speed $\omega$?

A flywheel is a rotating disc used to store energy. What is the maximum energy you can store on a flywheel built as a solid disc with mass 8 × 10⁴ kg and diameter 5.0 m, if it can spin at a max of 120 RPM?

When solid sphere 4 m in diameter spins around its central axis at 120 RPM, it has 10,000 J in kinetic energy. Calculate the sphere's mass.