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Fluid statics Buoyancy

  1. Nov 26, 2016 #1
    1. The problem statement, all variables and given/known data
    The rectangular gate shown in section is 3 m long (perpendicular to the paper) and is hinged about its upper edge B. The gate divides a channel leading to a fresh-water lake on the left and a salt-water tidal basin on the right. Calculate the moment, M, on the shaft of the gate at H required to prevent the gate from opening when the salt-water level drops to h = 1 m. Take the density of salt water 1050 kg/m3

    2. Relevant equations
    1. Force=rho*g*v
    2. F=gamma*h*a
    3.R= rho*g*h*a
    Where gamma = specific weight of liquid
    Where R=hydrostatic pressure

    3. The attempt at a solution
    Calculate Both forces acting on rectangle gate. Then solve for the moment
    Using sum of moments

    I am confused on which equation to use. I want to use 3. since its a flat surface but I confused whether to use gravity in the equation?

  2. jcsd
  3. Nov 26, 2016 #2
    On another note: In the attached png. I am confused on they calculated "3/2" for the height
    I am thinking if its the centroid?

    Attached Files:

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