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Homework Help: Fluid Mechanics and distance

  1. Jan 27, 2009 #1
    Im working on the problem below...

    http://img90.imageshack.us/img90/4939/dfadfgs5.jpg [Broken]

    Im having trouble finding the distance I have labled in the problem...H_c....which is the distance from the fluid surface to the center of the hatch......It appears to be found just using geometry but im not getting it....

    I found the area of the hatch to be .160 m....by adding the areas of the rectangle and two semi circles....and I have the specific weight found by multiplying (.90 x 9.81 Kn/m^3) = 8.83 Kn/m^3.......

    so the resultant force formula is

    F_r = specific weight x area x H_c......

    and the correct answer for the resultant force is 1213 N...but I cant get H_c...

    Also later in the problem I have to find the centroid of the hatch....so how would I go about doing that...would I take the centroid for each shape and average them?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 28, 2009 #2


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    Jason03: Study some trigonometry. I.e., memorize the definition of sine, cosine, and tangent for a right triangle. Remember those? You must learn those.

    The length of the slanted side would be (0.6 m)/cos(40 deg), right? See if you can figure out how to find H_c and F_r now.
  4. Jan 28, 2009 #3
    yea actually i figured it out shortly after i posted....but i did it slightly differently..

    Cos40 = y/.450

    Y= .450cos40

    Y= .344 m

    So ….(.6 +.6) - .344 = .855

    h_c = .855 m

    and the centroids were easily enough found by just adding the sum of the composites of a circle and square....

  5. Jan 28, 2009 #4


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    Nice work. That is a good approach you used.
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