1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Barrel and gauge pressure

  1. Jun 14, 2005 #1
    A barrel contains a layer of oil of thickness 0.110 m floating on water of depth 0.245 m. The density of the oil is 630 kg/m^3

    a) What is the gauge pressure at the oil-water interface?
    b) What is the gauge pressure at the bottom of the barrel?

    **
    a) Atmospheric Pressure + Pressure caused by oil = Total Pressure at oil-water interface
    Pressure caused by oil = density * depth * g
    Pressure caused by oil = 630 kg/m^3 * 0.11 m * 9.81 = 679.14 Pa
    Total Pressure = 101325 Pa + 679.14 Pa but still gives me the wrong answer

    ***The 101325 is atmospheric pressure which is exerted in addition to the pressure caused by the oil.

    b) Pressure at bottom = Pressure at oil-water interface + pressure caused by water
    Pressure caused by water = density * depth * g
    Pressure caused by water =1000 * 0.245 m * 9.8 = 2401
    P = 102004.833 Pa + 2401 Pa but still gives me the wrong answer

    ***The 102004.833 is the atmospheric pressure plus the pressure of the oil which is exerted on the bottom of the container in addition to the pressure caused by the water

    Please help
     
  2. jcsd
  3. Jun 14, 2005 #2

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    In your previous problem you did not include atmospheric pressure in the calculation. There is a reason for that. Pressure guages usually read the difference between the measured pressure and antmospheric pressure. In the current problem, the first reading should be just the pressure increase above 1 atmosphere due to the layer of oil. The second part should follow correctly from the first when you add the extra pressure from the water.
     
  4. Jun 15, 2005 #3
    The density of the oil is 630 kg/m^3 = 0.63 g/cm^3

    The pressure from the oil is 63g/cm^2 per meter depth
    At 0.11 m deep the pressure from the oil at the interface is 0.11 x 63 = 6.93 g/cm^2

    Water pressure is 100g/cm^2 per meter depth
    At 0.245 m deep the pressure from the water is 0.245 x 100 = 24.5 g/cm^2

    Pressure at the bottom of the barrel is 6.93 + 24.5 = 31.43 g/cm^2

    The units should be in Pa
    What do I do now?
     
  5. Jun 15, 2005 #4

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    Why did you convert the density units to g/cm^3 in the first place? If you work with the kg/m^3 units, your answer will come more naturally. Unit conversion is not difficult, but you should not need it in this problem.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Barrel and gauge pressure
  1. Gauge Pressure (Replies: 1)

  2. Gauge pressure (Replies: 5)

  3. Gauge Pressure (Replies: 2)

  4. Pressure gauge (Replies: 2)

  5. Gauge pressure (Replies: 8)

Loading...