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Physics Conceptual Question: Buoyancy?

  1. Feb 27, 2009 #1
    1. The problem statement, all variables and given/known data
    A fisherman and his young daughter are in a boat on a small pond. Both are wearing life jackets. The daughter 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. (If in the first the level Rises, and in the second it Falls, and for the rest one Cannot tell, enter RFCCCC)

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

    2. Relevant equations
    Archimedes Principle

    3. The attempt at a solution
    A) S because the balloon is above the water so isn't really adding any weight.
    B) S the anchor isn't touching the water
    C) C would the glass really make all that much a difference considering the volume of water involved...it's a pond.
    D) S He's floating so the water should't change
    E) R the water displaced is less than the weight of the object, the object will sink
    F) S Same as the father?
  2. jcsd
  3. Feb 28, 2009 #2


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    Homework Helper

    Hi Goodyearkl,

    Here are some thoughts on your reasons:

    But the balloon is affecting how much weight the water has to support.

    I'm not saying your answer is wrong, but I believe they mean the anchor is lowered into the water but not allowed to touch the bottom of the pond.

    This was supposed to be for part D, right? It won't make much of a difference (none of these will), but would it make any difference at all?

    Your reasons are right (if you mean that the weight of the water displaced by the object is less than the weight of the object); why would that make the water rise?
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