In an engineering laboratory an experiment was performed about convection. During the experiment a pure aluminum sphere is heated up to 500oC in an oven and it was removed from the oven and put in front of an air fan. The velocity of wind was 5m/s and the ambient air temperature was 40oC. After a while the temperature of the sphere decreased to 300oC.

 a. Determine the average rate of heat transfer from the ball. 

b. How long will it take to drop from 500oC to 300oC.

 c. Calculate the drag force (the relative roughness of the ball is 1.25x10-2 ).