20. Standard size screwdrivers can be used for which of the following purposes? (A) Removing and installing screws. (B) Prying off oil pans. (C) Hammering on tight parts. (D) All of the above.

There is a sweet potato with an initial uniform temperature of 25 c and it has an average diameter of 70 mm. thermal conductivity and diffusivity of the potato are 0.62 w/m c and 0.2 x 10^-6 m^2/s. respectively. it is to be cooled by refrigerated air at 1.8°c flowing at a velocity of 4 m/s. the average heat transfer coefficient between the potato and the air is 25 w/m2·°c. determine how long it will take for the center temperature of the potato to drop to 5.5°c