A solid brass sphere ( = 1.1.10-5 m/s, k = 61 W/m.C), 25 cm in diameter, is initially at T0 = 120 C. It is cooled by an air current to = 15 C. O The heat transfer coefficient between the air stream and the surface of the sphere is h = 500 W/m.C. Calculate: a) how long will it take for the center of the sphere to cool to 30C; b) what will be the initial energy uptake removed during this time