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Homework Help: Archemedes principle

  1. Mar 29, 2008 #1
    1. The problem statement, all variables and given/known data
    A fisherman and his young niece are in a boat on a small pond. Both are wearing life jackets. The niece is holding a large floating helium filled balloon by a string. Consider each action below independently, and indicate whether the level of the water in the pond R-Rises, F-Falls, S-Stays the Same, C-Can't tell.

    A) The fisherman fills a glass with water from the pond and drinks it.
    B) The fisherman knocks the tackle box overboard and it sinks to the bottom.
    C) The niece pops the balloon.
    D) The niece gets in the water, looses her grip on the string, letting the balloon escape upwards.
    E) The fisherman lowers himself in the water and floats on his back
    F) The fisherman lowers the anchor and it hangs vertically, one foot above the bottom of the pond.

    2. Relevant equations

    Use Archemedes principle

    3. The attempt at a solution

    I got SRRRSR (in order from A through F).
  2. jcsd
  3. Mar 30, 2008 #2

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    Can you explain how you got these? They may not be all correct.

    For example, ans to B should be F, i.e., level falls.
  4. Mar 30, 2008 #3
    I know they're not all correct, that's why I would like to see if anyone has a different answer.
  5. Mar 30, 2008 #4
    I don't think you can say for D. Does the girl float or sink?
    It looks like there are a couple of other problems also.
    Last edited: Mar 30, 2008
  6. Mar 31, 2008 #5

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    That's why I wanted you to explain your answers, so that we can discuss the errors, if any. We'll also know how much you have understood buoyancy and related stuff. Why don't you discuss briefly how you arrived at those conclusions?

    p.s. The human body sinks in fresh water, but just barely. It also depends on the fat content of that particular individual. Since we are considering a small pond, it's safe to say that in this case the niece is standing up in the water when she gets in the water. Anyway, we'll consider one particular case (sink or float) and base our understanding on that.
    Last edited: Mar 31, 2008
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