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Homework Help: Weight of the roof

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data

    A 190 km/h wind blowing over the flat roof of a house causes the roof to lift off the house.
    If the house is 6.5m x 15m in size, estimate the weight of the roof. Assume the roof is not nailed down.

    2. Relevant equations

    Bernoulli's equation : P1 + 1/2pv^2 +pgy = P2 + 1/2pv^2 + pgy

    3. The attempt at a solution

    i reduced the equation down to 1/2pv^2 to get pressure which numerically was 1671.3 and then i multiplied that by the area which i calculated to be 97.5 m^2, to get the force.

    I was clueless on how to approach this problem, but im even more confused now. please help.
  2. jcsd
  3. Nov 7, 2008 #2


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    Science Advisor

    You are done, aren't you? The problem asked for the weight of the roof. In order to lift something, you must apply a force (at least) equal to its weight. If the force you calculated was just enough to lift the roof, then that is the weight of the roof!
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