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Homework Help: Fluid Dynamics: Bernoulli's?

  1. Feb 25, 2012 #1
    attached is the problem. I use bernoulli's equation along a "streamline" from the inlet at point 1 to outlet at point 2. I do this to obtain the velocity V2. After working through it (simple algebra) I end up with 10.20 m/s ...seems right to me... however upon doing a conservation of mass analyses afterwards to get V3... I am getting 8.71 m/s this is nowhere on the multiple choice solution. This prof has been really really good at making sure the numbers are correct with very little round off error in the multiple choice options. It is possible that there is an error in the solutions but I think its more likely that I am doing something wrong.. Is it not correct to apply Bernoulli's equation to this example?

    Thanks for any help! this is driving me crazy!

    Attached Files:

  2. jcsd
  3. Feb 26, 2012 #2
    The question asks for the velocity at the upper section which you calculate as 10.2 m/sec.
    It is listed in the answers.
  4. Feb 26, 2012 #3
    ya sorry ..I phrased it poorly.

    I This question is part A. I can calculate a velocity 10.2 m/s which does appear on the list yes.

    However when I move to part B it wans to know what the velocity V3 of the lower section is.
    I use conservation of mass to determine this and i get an answer of 8.71. Which does not appear on the sheet. The closest is 8.60.

    So my question is, is it correct to apply Bernoulli's law to this problem, and can anyone else confirm an answer of 10.2? for V2?

    Thank you!
  5. Feb 26, 2012 #4

    rude man

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    No contradiction. If they had given you the length of the bottom pipe you could have written a bernoulli streamline equation for water running from A1 to A3. Combined with mass flow conservation (since you now know the mass flow at A1 and at A2) you could have solved for v3 and p3 also.
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