Explanation:
First find the properties of air. Then, convert all units to a consistent set (SI is usually simplest). For air at 20 degrees C, ρ =1.2 kg/m3, μ= 1.8x10-5 kg/(m s). The speed of the air is about 33 m/s. These give Re= 1.7 x 105. Refer to the figure on page 28 of the resource (Iowa) from subunit 6.4. This value of the Re puts the flow regime right in the transition to a turbulent boundary layer. Hence CD could be as little as 0.4 or as much as 1.2. If the surface of the flagpole is rough, then the lower limit is more likely. We then use F = CD ½ ρ v2 DL to calculate the range of the force experienced by the flagpole.
