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Homework Help: Helium balloon

  1. Mar 1, 2004 #1

    nsw

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    I can't seem to figure this simple helium balloon problem out? I would really appreciate some help? Thanks!

    Estimate the volume of a helium-filled balloon at STP if it is to lift a payload of 500 kg. The density of air is 1.29 kg/cubic meter and helium has a density of .178 kg/cubic meter.

    I think you use a formula like force bouyancy equals density of air times volume times gravity????????? but not quite sure.
     
  2. jcsd
  3. Mar 1, 2004 #2
    let V : Volume
    a= density of air
    b= density of He

    we have

    Code (Text):

     V*a=500*10[sup]3[/sup]+V*b
     
     
  4. Mar 1, 2004 #3

    nsw

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    How are you supposed to solve this equation with two unknowns?
     
  5. Mar 1, 2004 #4
    only V is unknown
     
  6. Mar 1, 2004 #5

    nsw

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    How do you solve

    V(1.29)= 500000+V(0.178)

    and is this really your answer?????????
     
  7. Mar 1, 2004 #6
    sorry the units of density are in Kg/m^3 so the equation will be

    (1.29-0.178)V=500

    V=450 m3
     
  8. Mar 1, 2004 #7

    nsw

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    Where does the 500 come from?
     
  9. Mar 2, 2004 #8
    isn't it the weight of the payload
     
  10. Mar 2, 2004 #9

    nsw

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    Oh Yah! Thanks a Bunch!
     
  11. Sep 15, 2004 #10
    New problem

    The values:
    Balloon diameter : 100 feet
    Balloon weight : 10,000 pounds
    Payload weight : 6,000 pounds
    Lifting gas : Helium
    Air density at ground level : .0625 lbs/cubic foot
    Temperature is constant

    At what altitude does the balloon fly?

    So far I've got:
    h = alpha [0.862 - (16,000 lbs/ mass of air)]

    I'm not even sure what the variables are, I was given 47 different formulas to determine the answer to this question, none of which are helping whatsoever.
     
    Last edited: Sep 15, 2004
  12. Sep 15, 2004 #11

    Chronos

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    Science Advisor
    Gold Member

    use bouyancy formula.
     
  13. Sep 15, 2004 #12
    Which is:

    mass of air (at Height, h) = [mass of payload+mass of balloon+mass of lifting gas]

    is that the right one?
     
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