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Homework Help: Water Pressure Homework Problem

  1. May 8, 2015 #1
    1. The problem statement, all variables and given/known data
    A person swim to certain depth in the ocean where the density of sea water is 1025 kg/m3. he does not have sophisticated equipment but he used an empty tube, the tube is L = 45.4 cm long and shaped like a cylinder. He wets the sides and then puts some sand in and shakes it around, coating the sides of the container. he was holding the tube vertically (the bottom is open the top is closed, allowing water to enter from the bottom) during the process. the person manages to wash away 10.9 cm of sand. How deep did the person dive?
    2. Relevant equations
    PV = nRT
    P = Pgh

    3. The attempt at a solution
    As Pi = 1.01*10^5 Pa and Vi = A*L, as Pi Vi =Pf Vf (as the temperature of the tube doesn't change in ocean). and Vf = A*(0.454 - 0.109). Pf = (Pi*Vi)/Vf = (Pi*L)/(L - 0.109)
    also Pf = P(density of sea water) gh, therefore h = (Pi*L)/((L - 0.109)*P(density)*g) = 13.2 m, but the answer is incorrect. could somebody help me please? Thanks in advance
  2. jcsd
  3. May 8, 2015 #2
    In determining Pf from the hydrostatic equation, you forgot to add in the surface pressure.

  4. May 8, 2015 #3
    Thank you very much!
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