During a recent thunderstorm the wind was blowing past your roof at 40 m/s. Assuming that the density of air is 1.20 kg/m^3, the size of the roof is 10m by 15m, and the air under the roof was at rest. What is the net force experienced by the roof? I know the answer is 1.44 x 10^5 N, I need to know how they got this answer.