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Need help identifying the force on a roof as a tornado wind passes over it.

  • Thread starter adlibitum
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  • #1
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Homework Statement



In a tornado or hurricane, a roof may tear away from the house because of a difference in pressure between the air inside and the air outside. Suppose that air is blowing across the top of a 2200 ft2 roof at 136 mph. What is the magnitude of the force on the roof?

Homework Equations



P1+gρh+.5ρv^2=P2gρh+.5ρv^2
P=F/A

The Attempt at a Solution



I tried to find the pressure above the roof, from Bernoulli's equation, take the difference in pressures above and below, and then divide that by the area...and that was very, very, very much the wrong thing, but I'm not sure why. I know that the answer is supposed to be on the order of x*10^5N.

Thank you!
 

Answers and Replies

  • #2
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
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If you take a pressure and divide by the area, you won't get force. Look at the units.
 

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