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Homework Help: Water Pressure in a lake

  1. Nov 15, 2009 #1
    1. The problem statement, all variables and given/known data
    At the surface of a freshwater lake the pressure is 106 kPa. (a) What is the pressure increase in going 34.5 m below the surface? (b) What is the approximate pressure decrease in going 36 m above the surface? Air at 20°C has density of 1.2 kg/m3.

    2. Relevant equations
    Ph20 = pgh
    Pabs = Ph20 + Patm

    3. The attempt at a solution

    I calculated both equations and got 439.4 kPa. I then subtracted 106 from 439.4 to get number one, but it doesn't work! How can I calculate number one? Also, I dont know where to begin for 2!
  2. jcsd
  3. Nov 15, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The pressure change in both cases can be calculated via ΔP = ρgΔh.
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