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Homework Help: Balloon Thread Height

  1. Feb 29, 2016 #1
    1. The problem statement, all variables and given/known data
    A heluim filled spherical balloon with a radius of 40 cm got tied into a uniform thread (uniform density) the threads length is 2 meters and its mass is 50 g the balloon ascends when left and ascends a the thread for h meters before it stabalizes again given the empty balloon's mass of 250 g and the density of is 1.29 kg / m^3 and heluim's density of 0.179 find h.

    2. Relevant equations
    I dont really know but I think we need to use Fb and pressure(pascal)

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Feb 29, 2016 #2
    Correct assessment so far. What is the mass per unit length of thread? If the thread is h meters long, what is the mass of the thread?
  4. Feb 29, 2016 #3
    50 grams as I stated
  5. Feb 29, 2016 #4
    You stated that, if its length is 2 meters its mass is 50 grams, and I asked, if its length is h meters, what is its mass. Do you see the difference???
  6. Feb 29, 2016 #5
    Sorry I might have not been clear but 50 grams is the entire thread's mass and the only one give for the thread the problem doesnt give the mass for the length h
  7. Feb 29, 2016 #6
    The first step in solving this problem is to determine from the information given what the mass of the string is if its length is h, rather than 2 meters.
  8. Feb 29, 2016 #7
    I cannnot seem to find a way to do that
  9. Feb 29, 2016 #8
    If 2 meters of the thread has a mass of 50 grams, what is the mass per unit length of thread (in grams per meter)?
  10. Feb 29, 2016 #9
  11. Feb 29, 2016 #10
    Good. Now, if the mass per unit length of the thread is 25 gm/m, and the length of the thread is h meters, what is the mass (in grams) of the thread (algebraically, in terms of h)?
  12. Feb 29, 2016 #11
    25 per m-h?
  13. Feb 29, 2016 #12
    It's 25h grams. So, if h = 2 m, for example, the mass is 50 gm, and if h is 12 m, the mass is 300 gm. Does that make sense now?
  14. Feb 29, 2016 #13
    yes but how do I find h ?
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