1. The problem statement, all variables and given/known data http://www.aapt.org/physicsteam/2010/upload/2010_FmaSolutions.pdf See Number 24 2. Relevant equations CoM = M1x1 + M2x2 / (M1+M2) MOI_disk: 1/2mr^2 3. The attempt at a solution So what I was thinking was find the new CoM then use the parallel-axis theorem. To find the new CoM: MsXs + MbXb / (Ms + Mb) = 0, where s is the small unshaded part, and b is the big, shaded portion. MsXs = - MbXb Xb = -Ms/MbXs Xb = (-R)(ρ∏R^2) / ρ(∏(2R)^2 - ∏R^2) Xb = R/3 Parallel Axis Theorem will smaller mass: 1/2MR^2 + 1/9MR^2 11/18MR^2 Yeah I'm pretty lost. I feel like there is a much better solution.