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Homework Help: Fluid pressure difference

  1. Dec 1, 2005 #1
    A patient is given an injection with a hypodermic needle 3.2 cm long and 0.25 mm in diameter. Assuming the solution being injected has the same density and viscosity as water at 20°C, find the pressure difference needed to inject the solution at the rate of 1.5 g/s.

    ok I have the equation V = [(P1-P2)(pi*r^4)]/(8*n*L)
    (P1-P2)= pressure difference
    r= .000125 m
    n= .0010055
    L= .032 m
    I do not know how I am suppose to transform 1.5g/s to m/s because im unsure of how to transfer grams to meters.... once i get that I can find the difference in pressure...

    In a similar problem with diameter being .28mm the answer came out to be 320kPa... help???
  2. jcsd
  3. Dec 1, 2005 #2


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    Homework Helper

    Pressure energy is converted into kinetic energy.
    To convert volume flow into velocity, you can consider:

    [tex]\dot{V}= A\cdot v[/tex]
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