A long copper rod of diameter 2.0 cm is initially at a uniform temperature of 100°C. It is now exposed to an air stream at 4°C with a heat transfer coefficient of 200 W/m2•K. How long would it take for the copper road to cool to an average temperature of 25°C? (Express the answers in seconds.) (Thermal properties of copper: k = 401 W/m·°C, rho = 8933 kg/m3, cp = 0.385 kJ/kg·°C.) s.