Thing is, (3/5)MR^2 > (1/2)MR^2, so whatever the mass of the disc, surely the total moment of inertia can only get greater than (3/5)MR^2 and never be reduced to (1/2)MR^2?
Hey,
I have recently come to this problem myself. After finding the moment of inertia for a spherical shell of radius R by starting with a solid sphere of radius R and taking out a solid sphere of radius R-r and them taking the limit r tends to 0, I thought I would try the same approach with...