A copper ball with a diameter of 2 cm is removed from an oven at a uniform temperature of 200°C. Upon removal from the oven, it is subjected to a flow of air at 1 atm and 20°C with a velocity of 8 m/s for a certain period of time so the surface temperature of the ball drops to 100°C. Determine (a) the average convective heat transfer coefficient; (b) the duration of the cooling process.