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Homework Help: Air Pressure and Water Pressure

  1. Nov 21, 2008 #1
    1. The problem statement, all variables and given/known data

    "At the surface of a freshwater lake the air pressure is 1.1 atm. At what depth under water in the lake is the water pressure 4.5 atm?"

    2. Relevant equations

    I used the equation Pgauge = Dgh

    3. The attempt at a solution

    I converted my atm to Pascals--> (4.5)(100000) = 450000 Pa
    Pguage = Dgh
    Pguage = (1000)(9.8)(h)

    -I used 1000, the density of water, but I'm not sure that is the right info to use for D!

    Then I solved for h.

    h = 450000/ (10000x9.8)
    h = 45.92
    I got it incorrect though. Can anyone offer any insight? Thanks!
  2. jcsd
  3. Nov 21, 2008 #2


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    Science Advisor
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    Gold Member

    That would have been OK if the problem asked for the gauge pressure. I think it's looking for the depth at an absolute pressure of 4.5 atm, which includes the atmospheric pressure.
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