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Fluids - pressure

  1. Nov 2, 2008 #1
    Fluids -- pressure

    Blood plasma flows from a bag through a tube into a patient's vein, where the blood pressure is 10 mmHg. The specific gravity of blood plasma at 37°C is 1.03. What is the minimum elevation the bag must have so the plasma flows into the vein?

    Prof gave this problem for us to solve, and I went through my notes and didn't see much that would help me get started.
    I got this equation P = P0 + density * g * h
    density = mass / volume

    Is this equation relevant to this problem?
    Im given the pressure 10 mmHg, gravity 1.03, but what is the density?
    I need to solve for height.

    Can someone help me get started?
     
  2. jcsd
  3. Nov 2, 2008 #2

    mgb_phys

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    Re: Fluids -- pressure

    'specific gravity' is the density compared to water, in this case 1.03* the density of fresh water (which is 1g/cc)
     
  4. Nov 2, 2008 #3
    Re: Fluids -- pressure

    Oh so the density is 1.03, then g would be 9.81m/s then.
    P = P0 + density * g * h
    10mmHg = 1.03 * 9.81m/s * h
    and solve for h?
     
  5. Nov 2, 2008 #4

    mgb_phys

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    Re: Fluids -- pressure

    Yes, make sure you have consistent units.
    (You also need the density of mercury.)
     
  6. Nov 2, 2008 #5
    Re: Fluids -- pressure

    where/how would the density of mercury come in?
    Im not too sure about this.
    They want the height in cm.

    10mmHg = 1.03 kg/m^3 * 9.81N/kg * h
     
  7. Nov 2, 2008 #6

    mgb_phys

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    Re: Fluids -- pressure

    You have a pressure of X cm of blood pushing down from the drip.
    You have a pressure equal to a column of mercury 10mm high pushing up.
    These pressures have to balance, you need to find X
     
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