A solid copper cube with sides 50 mm long is heated in a furnace to a uniform of 450 °C. The cube is than removed from the furnace and placed on a flat surface of low thermal conductivity, so that the heat transfer from the bottom face of the cube can be neglected, and allowed to cool in air at 25 °C. Calculate the time required for the temperature of the cube to fall to 300 °C. Take the thermal conductivity, specific heat capacity and density to be 390 W/(m.K), 410 J/(kg.K) and 7500 kg/m^3 respectively and the surface heat-transfer coefficient to be 5 W/(m^2.K) for the five exposed faces of the cube. Anye help would be greatly appreciated.