Spherical steel balls of diameter D 10 mm are cooled from an initial temperature of Th,i 1000 K by submersing them in an insulated oil bath initially at Tc, i 300 K. The total mass of the balls is mh 200 kg, while the mass of oil is mc 500 kg. The convection coefficient associated with the spheres and the oil is h 40 W/m2 · K, and the steel properties are kh 40 W/m · K, ph 7800 kg/m3, and ch 600 J/kg · K. Determine the steady-state ball and oil temperatures, and the time needed for the balls to reach a temperature of Th, f 500 K.