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Archimeded problem

  1. Oct 3, 2006 #1
    I can't really understand Archimedes principle..I mean i know how it works in water but i am totally clueless when it comes to air question.Here is a question:

    A balloon having a mass of 120 kg and volume of 400mcube is filled with helium gas of density 0.18kg m to the power of -3.The density of the surrounding air is 1.28kg m to the power of -3.What is the maximum load that can be lifted up by the balloon?Answer:320kg

    How do you solve this question?Also can someone please tell me how to count air question..My exam is a few days away:confused:
     
    Last edited: Oct 3, 2006
  2. jcsd
  3. Oct 3, 2006 #2
    dude draw the FBD of the balloon the lift force is pgv where p is density of air,g is 9.81 and v is volume of air displaced or u can say volume of balloon. i think u can find the ans from there right?
     
  4. Oct 3, 2006 #3
    I keep getting 392kg whereas the answer is 320kg.I have been spending an hour here
     
  5. Oct 3, 2006 #4

    Doc Al

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    Staff: Mentor

    Don't forget to consider the mass of the helium itself.
     
  6. Oct 3, 2006 #5
    so basically,you count the buoyancy force first and then later subtract the weight of the balloon and helium gas?
     
  7. Oct 3, 2006 #6
    hmm.....i got exactly 320kg maybe calculation error?
     
  8. Oct 3, 2006 #7

    Doc Al

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    Staff: Mentor

    Right. Whatever is left over is the additional load that can be lifted.
     
  9. Oct 3, 2006 #8
    oh,i see then..thank you everyone.Everyone have been a great help
    Just,one last question.The force acting downwards is the buoyancy force right?
     
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