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Homework Help: Fluid Dynamics

  1. Oct 1, 2007 #1
    Water flows out of a 13.0mm-diameter sink faucet at 2.30m/s.
    At what distance below the faucet has the water stream narrowed to 10 mm diameter?

    What I've done is that...
    I found A_1 (faucet) to be 0.0001327m^2
    and A_2 (bottom) to be 0.000314159m^2

    So I did the whole A_1*v_1 = A_2*v_2 thing
    and found v_2 to be 0.915m/s

    Then I plugged it in, into Bernoulli's equation
    1/2*rho*v_1^2 + rho*g*y_1 = 1/2*rho*v_2^2 + rho*g*y_2 (cancelling out the P_1 and P_2 because they.. cancel..)

    In which it is..
    0.5*1000*2.3^2 + 1000*9.8*y_1 = 0.5*1000*0,9715^2 + 1000*9.8*y_2

    2645 + 9800*y_1 = 471.906 + 9800*y_2
    9800*(y_1 - y_2) = -2174.094

    So.. h = 0.222m

    Or so I thought... It's wrong, so what am I doing wrong? Is it my A_1 and A_2's, etc.???
  2. jcsd
  3. Oct 1, 2007 #2


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    Staff Emeritus
    Science Advisor

    Check this number. What diameter was used?

    If the initial velocity is 2.3 m/s, how does one obtain 0.95 m/s for V2? The water accelerates with gravity.
  4. Oct 1, 2007 #3
    :D Thanks for the reminder that water accelerates with gravity
    That helped, and I got it :D
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