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Homework Help: Absolute Pressure in Multilayered Fluid

  1. Oct 1, 2006 #1
    I just can't figure this out:

    In a sample of seawater taken from an oil spill, an oil layer 3.4 cm thick floats on 61.3 cm of water. If the density of the oil is 750 kg/m^3, what is the absolute pressure on the bottom of the container?

    The density of water is 1000kg/m^3
    The density of oil is 750kg/m^3

    This is the approach I came up with:
    Pabs = Patm + Pwater + Poil

    Hoil = (3.4 cm * 1 m/100 cm = 0.034 m)
    Hwater = 61.3 cm * 1m/100 cm = 0.613 m

    equation:
    P = rgh
    r = density; g = gravity constant (9.8 m/s^2); h = height

    Poil = 750 kg/m^3 * 9.8 m/s^2 * 0.034 m = 249.9 Pa
    Pwater = 1000 kg/m^3 * 9.8 m/s^2 * 0.613 m = 6007.4 Pa
    Patm = 101300 Pa
    Pabs = 101300 Pa + 249.9 Pa + 6007.4 Pa = 107557.3 Pa

    however I'm not too sure. I don't remember what exactly was said in class.
    This is the other way which could be right.
    Hoil + Hwater = 0.034 m + 0.613 m = 0.647 m
    Pgauge = density of oil * g * h
    Pgauge = 750 kg/m^3 * 9.8 m/s^2 * 0.647 m = 4755.45 Pa
    Pabs = Patm + Pgauge
    Pabs = 4755.45 Pa + 101300 Pa = 106055.45 Pa
     
  2. jcsd
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