Physics help moment of inertia?

Question

An energy storage system based on a flywheel (a rotating disk) can store a maximum of 3.7 MJ when the flywheel is rotating at 2.0×10^4 revolutions per minute.

Part A

What is the moment of inertia of the flywheel? In kg * m^2

Answer 1

KE = 1/2 Iw^2; where I is the inertia you are looking for, w = 2E4 rev/min = 2E4*2pi/60 rad/sec, and KE = 3.7E6 Joules max, which is the angular kinetic energy

Solve for I = 2KE/w^2 = 2*3.7E6/(2E4*2*3.141569/60)^2 = 1.687023111 kg-m^2