Chapter 6, Problem 6.49P

A thin, flat plate that is $0.2\text{m}\times 0.2\text{m}$ on a side with rough top and bottom surfaces is placed in a wind tunnel so that its surfaces are parallel to an atmospheric airstream having a velocity of 30 m/s. The air is at a temperature of $T_{\infty }=20°\text{C}$ while the plate is maintained at $T_s=80°\text{C}\text{.}$ The plate is rotated $45°$ about its center point, as shown in the schematic. Airflows over the top and bottom surfaces of the plate, and measurement of the heat transfer rate is 2000 W. What is the drag force on the plate?