I'm not sure if this is the right place to ask this, but I'll try here... [I'm not physics student and don't know how to differentiate "intro physics" from "not intro physics"] I'm asked to calculate moment of inertia [around center of mass] for a thick disk. The problem: I calculate the moment of inertia in two different ways and get different answers. Way 1 [the crazy method] - I calculate moment of inertia for some inner part of the disk then I calculate the moment of inertia for the rest of the disk. Way 2 [the standard method] - I calculate the moment of inertia of the whole disk continuously. The mass of the outer disk is M/2 and so is the mass of the inner disk. It is hard to to draw thing in the forums so I'm attaching my drawings and calculations as a picture: link.