A thick casting with a thermal diffusivity of 5 x 10-6 m2/s is initially at a uniform temperature of 150oC. One surface of the casting is suddenly exposed to a high-speed water jet at 20oC, resulting in a very large convective heat transfer coefficient (Hint: assume imposed surface temperature). The thermal conductivity of the casting is 20 W/m-K. Determine the temperature 20 mm in from the surface after 40 seconds. Check your answer using an alternative technique. Your final answer should be about 101.3 oC.