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I dont understand this

  1. May 15, 2006 #1
    A 120 foot high dam is shaped by the symmetric function y = 2x^(4/3). The water level is at the top of the dam. Set up an integral that gives the total water pressure against the dam. Water weights 62.5 lbs per cubic foot.

    S = integral sign

    P = F / A

    but teacher's answer is

    120
    S 62.5(120-y)*2(y/2)^(3/4)dy
    0

    I understand the 2(y/2)^(3/4)dy part, its the area, but I dont get what is
    62.4(120-y), its seems to me that the teacher is doing P = F * A, which is wrong... if I m not wrong... please help me clear this... Final coming!!!
     
  2. jcsd
  3. May 15, 2006 #2

    Doc Al

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    Staff: Mentor

    What you are probably asked to find is the total force on the dam due to the water pressure. The teacher is doing F = P * A (not P = F * A, which would indeed make no sense). 62.4(120-y) gives the water pressure as a function of vertical position (measured from the bottom of the dam).
     
  4. May 16, 2006 #3

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    There is no such thing as "total pressure". As Doc Al said, the problem clearly is asking for "total force" against the dam. And it is correct that F= P*A.
     
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