This problem involves a cylinder falling inside a pipe that is filled with oil, as depicted in the figure. The small space between the cylinder and the pipe is lubricated with an oil film that has viscosity $.$ Derive a formula for the steady rate of descent of a cylinder with weight $W,$ diameter $d,$ and length $l$ sliding inside a vertical smooth pipe that has inside diameter $D.$ Assume that the cylinder is concentric with the pipe as it falls. Use the general formula to find the rate of descent of a cylinder $100mm$ in diameter that slides inside a $100\mathrm{.}5mm$ pipe. The cylinder is $200mm$ long and weighs $15N.$ The lubricant is SAE $20W$ oil at $10C.$