What is the net force on the roof

AI Thread Summary
The discussion revolves around calculating the net force on a flat roof due to wind blowing at 35 m/s over an area of 240 m². The relevant equations include total pressure, which combines atmospheric pressure and dynamic pressure from the wind. The initial calculation yielded a net force of 24,200,000 N, but the correct answer provided was 1.9 * 10^5 N. It was clarified that only the dynamic pressure term across the roof area should be considered for the net force calculation. The final calculation confirms that the dynamic pressure is the key factor in determining the net force on the roof.
robvba
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Homework Statement


If wind blows at 35 m/s over a house, what is the net force on the roof if its area is 240 m2 and is flat?



Homework Equations



Pat + 1/2 * pair * v^2

The Attempt at a Solution


wind velocity - v - 35
area of roof - A - 240
density of air - p - 1.29
atmospheric pressure - Pat - 100,000

Fnet=?

P = total pressure = Pat + 1/2 * p * v^2
Fnet = P * A = 24,200,000 N

but answer provided was 1.9 * 10^5 N
 
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Aren't you just interested in the dynamic pressure term across the area of the roof?

1/2 * 1.29 * 352 * 240 = ...
 
yes i am :)
 

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