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Homework Help: Fluid Dynamics - Calculate the resultant moment

  1. Aug 27, 2013 #1
    1. The problem statement, all variables and given/known data

    A rigid vertical wall separates two liquid reservoirs. The first reservoir contains oil of density p=864 kgm-3 at a height of 6m above the ground, while the second reservoir contains water (1000kgm-3) at a height of 5m from the reservoir bottom. Calculate the resultant moment, at the bottom of the vertical wall.


    2. Relevant equations

    FR = PCA = pgycA

    3. The attempt at a solution

    Area is not given so I will take that out of the equation

    water = 1000*9.81*5/2 *5/3
    oil = 864*9.81 *6/2*6/3

    Answer = 50855 - 40875 = 9.98 n.M

    I think that the answer is right but I am not sure as to why it is right. Can someone please verify and explain. Thank you
    Last edited: Aug 27, 2013
  2. jcsd
  3. Aug 27, 2013 #2


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Mtrn_engineer! Welcome to PF! :wink:

    (I think the question is probably asking for the moment per mass, so you'll be factoring out an m = ρAL somewhere)

    Call the area A, and slice each side into horizontal slices of area A thickness dh and depth h …

    then find the moment for that slice, and then integrate wrt h.

    Show us what you get. :smile:
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