2.23 A long cylindrical rod of radius R=5cm and k=20W/m.°C contains radioactive material which generates energy uniformly within the cylinder at a constant rate of ġ.=2x105W/m³. The rod is cooled by convection from its cylindrical surface into the ambient air at T=20°C with a heat transfer coefficient h=50W/m².°C. Determine the temperatures at the center and the outer surface of this cylindrical rod.