A wind with a speed of $30 \mathrm{~m} / \mathrm{s}$ blows parallel to the flat roof of a house. The

Question

A wind with a speed of $30 \mathrm{~m} / \mathrm{s}$ blows parallel to the flat roof of a house. The area of the roof is $200 \mathrm{~m}^{2}$. Assuming that the pressure inside the house is atmospheric pressure, the aerodynamic force exerted by the wind on the roof and its direction will be ($ho_{	ext{air}} = 1.2 \mathrm{~kg} / \mathrm{m}^{3}$)

Professor PC Thomas Classes · Answer

(d) : According to Bernoulli's principle, the high-speed wind above the roof creates a region of low pressure. The pressure difference is $\Delta P = \frac{1}{2} ho v^2 = \frac{1}{2} 	imes 1.2 	imes (30)^2 = 0.6 	imes 900 = 540 \mathrm{~Pa}$. The force exerted on the roof is $F = \Delta P 	imes A = 540 	imes 200 = 108000 \mathrm{~N} = 1.08 	imes 10^5 \mathrm{~N}$. Since the pressure inside is greater than the pressure outside, the net force acts upwards.