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Homework Help: Fluid Dynamics of saltwater in sealed tank

  1. Dec 11, 2011 #1
    1. The problem statement, all variables and given/known data
    A sealed tank containing seawater to a height of 12.8 m also contains air above the water at a gauge pressure of 2.90 atm. Water flows out from the bottom through a small hole.

    How fast is this water moving?

    2. Relevant equations
    I believe that Bernoulli's equation is to be applied here somehow.

    3. The attempt at a solution
    I hate that I don't have more work to show, but I really don't know how to approach this one at all.

    [tex]p_1 + \frac{1}{2}ρV_{1}^{2} + ρgh_{1}= p_2 + \frac{1}{2}ρV_{2}^{2} + ρgh_{2}[/tex]

    I'm not really sure how to apply this for this type of problem. The gauge pressure air at the top is confusing me. The other questions I have worked on so far were all liquids moving through pipes and such, where the application of the equation is apparent. Can someone just point me in the right direction here?
  2. jcsd
  3. Dec 11, 2011 #2
    Guage pressure is, of course, pressure above atmospheric pressure. And the "small hole" is at atmospheric pressure. Whence,

    P1 - P2 = 2.9 atm.

    And since the problem says the outlet is a small hole, it is reasonable to assume:

    V1 ≈ 0.
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