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Homework Help: Fluid Mechanics- Pressure on a gate

  1. Sep 16, 2012 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations


    Ycp=bh3/(12)(h/2)b + (h/2)

    3. The attempt at a solution

    I found the angle of the gate from the horizontal to be 53.1 degrees. Using this, I found y to be 2.5m and H (vertical distance to centroid) to be 6 m (2.5sin(53.1)+4).

    I then found Fw=9810*6*(4*5)=1177200N, and Ycp=(4*53)/(12*20*2.5) +2.5=3.33m.

    By taking the moment at the ground, I found Fw*(5-3.33)-5P=0, so P= 393kN. My book says the answer should be 523 kN. Help please.
  2. jcsd
  3. Sep 16, 2012 #2

    rude man

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    Homework Helper
    Gold Member

    The picture does not show the angle P makes with the horizontal or vertical, so the question looks unanswerable to me. P could be an angle perpendicular to the 5m line or at some angle away from perpendicularity.
  4. Sep 16, 2012 #3
    I believe that P is supposed to be perpendicular surface (opposing Fw)
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