A disk-shaped flywheel, of uniform density r, outer radius R, and thickness w, rotates with an angular velocity v, in rad/s. For a steel flywheel rotating at 3000 RPM, determine the kinetic energy, in N ? m, and the mass, in kg, if R 5 0.38 m and w 5 0.025 m. Determine the radius, in m, and the mass, in kg, of an aluminum flywheel having the same width, angular velocity, and kinetic energy.