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

  1. Nov 3, 2011 #1
    1. The problem statement, all variables and given/known data

    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?

    2. Relevant equations

    P1+gρh+.5ρv^2=P2gρh+.5ρv^2
    P=F/A

    3. 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!
     
  2. jcsd
  3. Nov 4, 2011 #2

    SteamKing

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    Staff Emeritus
    Science Advisor
    Homework Helper

    If you take a pressure and divide by the area, you won't get force. Look at the units.
     
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