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Thermodynamics Question

  1. Aug 27, 2005 #1
    OK, I have been working on this for a while.

    I have a balloon, filled with helium.
    mass = 140 kg
    density(air) = 1.16 kg/m^3
    density(He) = 1/7*density(air)
    diameter of balloon = 10 m
    bouyant force = density(air)*g*Volume(balloon)
    weight = m*g
    net force = bouyant force - weight = ma

    I need to solve for a. The book tells the answer (16.5 m/s^2), so I know what I need to get to, but doing the steps above, I haven't gotten close.

    Anybody have any ideas to help out?

  2. jcsd
  3. Aug 27, 2005 #2


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    Science Advisor
    Homework Helper

    You need the mass of the 'entire' balloon, that is, the mass of the container itself which is 140 kg, plus the mass of the helium inside. I think that's about the only point where it can really go wrong.
    Why don't you post what you got for the volume and mass of the balloon and what you got for the bouyancy.
  4. Aug 27, 2005 #3
    ok, volume was 523.6 m^3, mass ended up being 226.768 kg.

    i had forgot the mass of the helium, i got the right answer now, thanks!!!
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