What is the force exerted on a flat roofed building by wind pressure?

[ku1005]

Homework Statement

"Wind (density=1.29kgm^-3) blows over a flat roofed building of height 20m at 12ms^-1.The area of he roof is 100m^2.What is the magnitude and direction of the force exerted on the roof if the pressure difference between inside and outside is due solely to the fact that the inside air is still?Assume laminar flow."

Homework Equations

Im really stumped with this Q, I have scanned the net and it seems to involve the Bernoulli Eqn , however, i don't really understand what's occurring, any help appreciated.

The Attempt at a Solution

 

[siddharth]

If you assume that the thickness of the roof is negligible, what's the pressure of the air just outside the roof, where the air is flowing? And the pressure inside where the air is stationary? So, what's the force due to the pressure difference?

 

[ku1005]

thats the thing, i undererstand where the pressure difference comes from, but not how to calculate it based on the dimensions of the roof?...

 

[siddharth]

The dimensions of the roof is needed to calculate the force due to the pressure difference. You need to use Bernoulli's equation to calculate the pressure difference. (Hint: The air inside is stationary, while outside, it's moving.)