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Fluid mech problem

  1. Dec 9, 2006 #1
    I have a 4" hose attached to a 2" nozzle, me resistance coeffient of the nozzle is .12, and the jet of water exiting the nozzle is 24.4 m/sec. The water is flowing from the 4" to the 2". What I am having trouble finding is Pressure 1 and the the velocity 1.

    What I know is that P2=0, areas of the hose is 4" = 12.56 in^2 converts to .008m^2, 2" = 3.14 in^2 converts to .002m^2, I think Q=V2*A2 = 24.4*.002= .049 m^3/sec

    then v1= 6.125 m/s?
    then would I plug this into the bernoulli's equ.??

    Thank You
  2. jcsd
  3. Dec 10, 2006 #2


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    Science Advisor

    Use the continuity equation to calculate the upstream velocity. If you know the velocity at the downstream loacation, this would equate to a certain mass flow rate. The mass flow rate will remain constant. So, since this is water and density can be considered constant, you have the old area, the density and the only unknown would be the velocity.

    For the second part, once you have the upstream velocity, you can use Bernoulli to calculate the upstream pressure.
  4. Dec 10, 2006 #3
    I was basically on the right track

    thank you
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