1. The problem statement, all variables and given/known data A spherical tank of radius 8 feet is half full of oil that weighs 50 pounds per cubic foot. Find the work required to pump oil out through a hole in the top of the tank. 3. The attempt at a solution this is an example problem in my book and they start off by subdividing the region into disks of thickness Δy and radius x and by saying as a result of the increment of force for each of these disks being given by weight we have ΔF = weight → (50pounds/ft3)*volume → 50(∏x2Δy)pounds. This is where I get stuck, I have no idea where that expression, ∏x2Δy, came from. Are they using ∏r2h here for the volume of each cylindrical shell?