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Homework Help: Volume Flow Rate, Help?

  1. Nov 5, 2008 #1
    Volume Flow Rate, Help???

    1. The problem statement, all variable and given/known data

    The volume flow rate in an artery supplying the brain is 3.5E-6 m^3/s.

    (a.) If the radius of the artery is 5.4E-3 m, determine the average blood speed.
    (b.) Find the average blood speed at a constriction in the artery if the constriction reduces the radius by a factor of 7. Assume that the volume flow rate is the same as in part (a.)

    2. Relevant equations

    Q = Volume flow rate = AV

    3. The attempt at a solution

    I got (a.) but I need help with (b.). I think my radius for part (b.) is wrong, but I don't know how else to get it.

    For part (a.) I got 0.0382 m/s by using

    Q = Volume flow rate = AV = pi x r^2 x v = 3.5E-6 m^3/s

    and using the given radius in part (a.) I solved for v.

    For part (b.) I divided the given radius by 7, and subtracted that from the original radius to get a radius of 4.63E-3, and I put it into the equation the same way as part (a.) and I got 0.0520 m/s, but it's wrong. Help?
    Last edited: Nov 5, 2008
  2. jcsd
  3. Nov 6, 2008 #2


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    Re: Volume Flow Rate, Help???

    They mean that the constricted radius is 1/7 of the original radius, not 6/7 of it.
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