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Homework Help: Calculating the gauge pressure?

  1. Mar 2, 2010 #1
    1. The problem statement, all variables and given/known data
    Water flows through a .259m radius pipe at the rate of .125m^3/s. The pressure in the pipe is atmospheric. The pipe slants downhill and feeds into a second pipe with a radius of .190m, positioned .796m lower. What is the gauge pressure in the lower pipe? The acceleration of gravity is 9.81 m/s^2. Answer in the units of Pa.

    2. Relevant equations
    A1V1 = A2V2
    flow speed = flow rate / area
    P1 + [(Rho)(g)(h1)] + [(1/2)(rho)(V1^2)] = P2 + [(Rho)(g)(h2)] + [(1/2)(rho)(V2^2)]

    3. The attempt at a solution
    Calculating the flow speed gives me V1. Then I can find V2 using the equation of continuity.
    Also, because we are looking for gauge pressure, I am look for P1- P2. Therefore:

    P1-P2 = [(rho)(g)(delta H)] + [(1/2)(rho)(V2^2)] - [(1/2)(rho)(V1^2)]

    Is this correct? Also, do I need to do anything for P1 if that pressure is atmospheric in the pipe? Thanks in advance.
  2. jcsd
  3. Mar 2, 2010 #2
    Anybody? Just tell me if what I am doing is correct.
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