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Homework Help: Fluid Mechanics -Momentum Equation

  1. Sep 23, 2012 #1
    Fluid Mechanics --Momentum Equation

    1. The problem statement, all variables and given/known data
    A large weigh tank is to be used in the calibration of a flow metre. Measurements of weights as a function of time are to be made. Water enters the tank vertically from the flow metering system at a speed of 20 ft/s through a 1.5 in. diameter pipe. If the weight of the empty tank is 50 lbf, determine the scale reading at t=10 s.

    I found the reading to be 74.8 lbf but the answer is 212.67 lbf.

    Any help is appreciated.

    The link to my working.

  2. jcsd
  3. Sep 23, 2012 #2
    Re: Fluid Mechanics --Momentum Equation

    I am unable to decipher your link. Without considering the change in momentum of the water, I get about 203 pounds. If the pipe discharges vertically downward, you'll have to consider momentum change of the water adding to the weight of the vessel.
  4. Sep 23, 2012 #3
    Re: Fluid Mechanics --Momentum Equation

    Thanks for the reply.
    I have already solved the question. Turned out there's a mistake when I calculated
    the weight of water after 10 seconds and I did not include the gc factor. And yes,
    momentum of the falling water is already included in the momentum equation.
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