A wind with speed 40 m/s blows parallel to the roof of a house. The area of the roof is 250$m^2$. Assuming that the pressure inside the house is atmospheric pressure, the force exerted by the wind on the roof and the direction of the force will be

$\left({\rho }_{\text{air }}=1.2 \mathrm{kg}/{\mathrm{m}}^3\right)$

 

The pressure difference between the points just inside and outside the house creates a force towards the lower pressure side.
According to Bernoulli’s principle,
$\mathrm{P}+\frac{1}{2}\rho {\mathrm{V}}^2=\text{constant}$

Where p is pressure, $\rho$ is density,
V is the velocity of air.
$\Rightarrow P_{\text{atm}}+\frac{1}{2}\rho V_{\text{in}}^2=P_{\text{out}}+\frac{1}{2}\rho V_{\text{out}}^2$
$\Rightarrow P_{\text{otm}}-P_{\text{out}}=\frac{1}{2}\rho V_{\text{out}}^2$
$=\frac{1}{2}\times \left(1.2{\mathrm{kgm}}^{-3}\right)(40\mathrm{m}/\mathrm{s}{)}^2$

$=960{\mathrm{kgm}}^{-1}{\mathrm{s}}^{-2}$

This pressure difference causes the upward force F.
$F=(P_{\text{atm}}-P_{\text{out}})\times A=960\times 250=2.4\times {10}^5\mathrm{N}$