1. The problem statement, all variables and given/known data 2. Relevant equations τ = μ (du/dy) 3. The attempt at a solution For part B) dM = τr dA τ = μ (rΩ/Δr) ∫ (μrΩr2πr / Δr)dr = μR4πΩ / 2Δr pretty sure that's correct. I'm confused for part A though. I want to set it up as dM = τR dA = τR (2πRdL) and τ = μ (RΩ/L) substitute and integrate over 0 to L. But this doesn't yield the correct result.