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Hydrostatics Problem (Why is this Wrong?)

  1. May 16, 2009 #1
    Picture1-32.png

    In calculating the vertical force component, you want to find the weight of the missing water.

    This should be simple: Find the Volume of the missing water and multiply by specific weight.

    Why is my volume calculation incorrect? I am using the volume of the rectangular prism whose top coincides with the surface and whose base coincides with B. Then I subtract the volume of the quarter cylinder:

    [tex]V_{Tot}=V_{rect}-.25V_{cyl}[/tex]

    [tex]V_{rect}=(1.5+0.75)(0.75)(1.2)[/tex]

    [tex].25*V_{cyl}=.25*(\pi (0.75)^2(1.2)[/tex]

    But this does not give the correct volume. The solution says to use:


    I am failing miserably to see how my method is different from theirs? Am I messing up a dimension here?
     
  2. jcsd
  3. May 17, 2009 #2
    Aaahhhhhhhh!!!!! My brain!!!!!!

    Edit: How does what they wrote even make any sense?

    The first term has dimensions of m^3 and the second has dimensions of m^2 !

    Not to mention, if you put those numbers into your calculator they do not equal what they are saying they equal. WTF
     
    Last edited: May 17, 2009
  4. May 17, 2009 #3

    Doc Al

    User Avatar

    Staff: Mentor

    It looks like the second term in their solution has a typo: They left off the factor of 1.2m.
     
  5. May 17, 2009 #4
    Yeah. I think that makes it equivalent to mine if you tack that on.

    Sometimes it does not help to be able to check your answers. :grumpy:
     
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