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Homework Help: Pressure gauge

  1. Jun 10, 2009 #1
    1. The problem statement, all variables and given/known data

    Water flows at 3.64 L/s through a horizontal pipe that narrows smoothly from 10.2 cm diameter to 4.89 cm diameter. A pressure gauge in the narrow section reads 47.0 kPa. What is the reading of a pressure gauge in the wide section?

    2. Relevant equations


    P1+ [tex]\rho[/tex]gh+0.5*[tex]\rho[/tex]V2=P2+[tex]\rho[/tex]gh+o.5*[tex]\rho[/tex]V2

    3. The attempt at a solution

    so first thing i did was convert 3.64L/s to 3.64x10-3 m3/s
    and then found the area of each part of the opening. since they tell me the gauge reading at the narrow end (4.89cm) i used F=PA to find the force. using this force and the area of the wide end (10.2cm) i got a P. this was wrong..can someone tell me what i'm doing wrong??
  2. jcsd
  3. Jun 10, 2009 #2


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    Science Advisor
    Homework Helper

    Hi brunettegurl! :smile:

    (have a rho: ρ :wink:)

    I'm confused … what does force have to do with it? :confused:

    Use conservation of mass to find the speeds, and then use Bernoulli's equation :smile:
  4. Jun 10, 2009 #3
    thanks i realized that after i redid what i did
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