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Homework Help: Venturi meter help

  1. Aug 12, 2008 #1
    Venturi meter help!!!

    1. The problem statement, all variables and given/known data
    A venturi meter is measuring the flow of water; it has a main diameter of 3.0 cm tapering down to a throat diameter of 1.0 cm. If the pressure difference is measured to be 16 mmHg, what is the speed of the water entering the venturi throat?


    2. Relevant equations

    -+P_2+%7D+%5Cright%29%7D%7D%7B%7B%5Crho+%5Cleft%28+%7BA_1%5E2+-+A_2%5E2+%7D+%5Cright%29%7D%7D%7D.gif

    Got that equation from a previous part of the problem where it asked me to "Show that the flow speed measured by a venturi meter (see Figure 13–32 in the textbook) is given by the relation"

    3. The attempt at a solution

    I used [tex]\rho[/tex] to be density of water. I converted the diameters to radius in meters. I converted the pressure to "m-Hg". I get 1.77*10^-5. The homework program keeps telling me I'm wrong. I can't see what I'm doing wrong. Thank You for the help!
     
  2. jcsd
  3. Aug 13, 2008 #2

    tiny-tim

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    Homework Helper

    Hi ahello888a! :smile:

    (you said mmHg as the top, and m Hg at the bottom … is that a typo?)

    erm … we need to see your full calculation if we're going to find out where it's wrong! :wink:
     
  4. Aug 13, 2008 #3

    stewartcs

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    Science Advisor

    Re: Venturi meter help!!!

    Start by writing out the energy balance using the Bernoulli equation.

    Hints:
    Assume the elevation change is zero.
    Neglect the small friction.
    Use the continuity equation.

    Hope this helps.

    CS
     
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