Along iron rod (rho = 7870 kg/m3, cp = 447 j/kg·k, k = 80.2 w/m·k, and α = 23.1 × 10−6 m2/s) with diameter of 25 mm is initially heated to a uniform temperature of 700°c. the iron rod is then quenched in a large water bath that is maintained at constant temperature of 50°c and with a convection heat transfer coefficient of 128 w/m2·k. determine the time required for the iron rod surface temperature to cool to 200°c. solve this problem using the analytical one-term approximation method.