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Homework Help: Hard fluid problem

  1. Jan 9, 2008 #1
    A pump, submerged at the bottom of a well that is 35 m deep, is used to pump water uphill to a house that is 50 m above the top of the well. The density of water is 1000 kg/cm^3. All pressures are gauge pressures. Neglect the effect of friction, viscosity.

    A) REsidents of the house use .35 m^3 of water per day. The day's pumping is completed in 2 hours during the day.
    1) calculate the minimum work required to pump the water used per day
    2) Calculate the minimum power rating of the pump

    B) The average pressure the pump actually produces is 9.2X10^5 N/m^2. Within the well the water flows at .50 m/s and the pipe has a diameter of 3cm. At the house the pipe diameter is 1.25cm
    1) Calculate the flow velocity when a faucet in the house is open
    2) Explain how you could calculate the minimum pressure at the faucet

    picture here, problem #6

    attemp solution
    1- M=DV
    M=1000(.35)= 350kg = 350000g
    W=350000(9.8)(30+50) 30from bottom to ground, 50 from ground to the house
    2- P=W/t
    P= 274400000J/7200s 2hour=7200s
    P=38111.1 Watt

    1- AV=AV
    (.03/2)^2*pi*.05= (.0125/2)^2*pi*V
    V=2.88 m/s
    2- P=F/A
    I know the area, but i dont know how to get the F,

    I need a confirm, or any suggestion
  2. jcsd
  3. Dec 16, 2008 #2
    I'm doing this problem as well!
    I just wish to comment on something.
    Why did you convert 0.35m^3 to 350000g?
    Everything else is in kg... and
    on part A1 doesnt h=35+50=85?

    Now I think the solution to P=F/A

    and from Rho(density)=m/V
    and a=g

    I hope this makes sense.
  4. Dec 18, 2008 #3
    Note: (rho) = density - in this case of water
    W=291550 Joules

    Note 2hrs = 7200s
    P=40.5 watts

    Next one you have done correctly..
    V2 = 2.88 m/s

    Last one.. You must use bernoullis principle
    P is given, rho = density of water(1000kg/m**3)
    v = 2.88 m/s, g is 9.8, h is 85m

    What you were doing wrong was not converting units properly
    Always stick to m, kg, s
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