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Why Cant I Figure this stuff out

  1. Oct 3, 2004 #1
    I need to tell wether the water level rises, falls, is unchanged, or cat tell. The father and son are in a boat wearing lifejackets.

    The son pops a helium filled balloon that he is holding by a string.
    (Id say unchanged since the ballon is floating in the air right)

    The fisherman fills a glass with water from the pond and drinks it.
    (No idea, but i would guess that it stays the same since the weight is being put back into the fisherman)

    The fisherman lowers himself in the water and floats on his back.
    (Raises because more water is being displaced now?)

    The son gets in the water and pops the floating helium ballon
    (Raises because the son is displacing water?)

    The fisherman knocks the tackle box overboard and it sinks to the bottom.
    (Falls because the tacklebox was floating in the boat, now it is skinking to the bottom and displacing less water)

    The fisherman lowers the anchor and it hangs one foot above the bottom of the pond
    (Falls, same reason as above)

    but my answer is wrong and I dontknow where, please help

    Thankyou
     
  2. jcsd
  3. Oct 3, 2004 #2
    you are confusing the concepts of weight and volume.
     
  4. Oct 3, 2004 #3
    i dont understand, the only area where i mentioned weight was in the glass of water, i tried all possible answers for that one, but there are other ones wrong

    could you tell me a set of rules or explain it more so that i can understand it better?

    thanks
     
  5. Oct 3, 2004 #4
    Ok i have revised my answer but it is still wrong, could you please tell me which ones are wrong

    The son pops a helium filled balloon that he is holding by a string.
    (Id say unchanged since the ballon is floating in the air right)

    The fisherman fills a glass with water from the pond and drinks it.
    (No idea, but i would guess that it stays the same since the weight is being put back into the fisherman)
    im confused on this one

    The fisherman lowers himself in the water and floats on his back.
    (Raises because more water is being displaced now?)
    unchanged because the displacing bodies are still the boat + the fisher

    The son gets in the water and pops the floating helium ballon
    (Raises because the son is displacing water?)
    unchanged because the displacing bodies are still the boat + the son


    The fisherman knocks the tackle box overboard and it sinks to the bottom.
    (Falls because the tacklebox was floating in the boat, now it is sinking to the bottom and displacing less water)

    The fisherman lowers the anchor and it hangs one foot above the bottom of the pond
    (Falls, same reason as above)
    unchanged because the anchor is still pulling the boat down
     
  6. Oct 3, 2004 #5
    this is the only problem i am still having trouble with, ive been reading as much as i can on the internet and cant seem to get the correct answer, if anyone could explain each situation to me, that would be great
     
  7. Oct 4, 2004 #6
    can anyone help?
     
  8. Oct 5, 2004 #7
    well this question is due in 8 hours and I still cant figure it out. This will be the last time i bump it up to try and get an answer. Can i please get some help here?
     
  9. Oct 5, 2004 #8

    NateTG

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    Science Advisor
    Homework Helper

    OK:
    If the amount of weight that's being floated increases, the water level rises. If the amount of weight being floated decreases, the water level drops. If the amount of weight being floated doesn't change, then the water level stays the same as well.

    All you have to figure out is if more weight, less weight, or the same amount of weight is being floated.
     
  10. May 11, 2005 #9
    Can someone please check my answers? There are the choices Rise Falls Stays the same and Cannot Tell.


    A) The fisherman fills a glass with water from the pond and drinks it.

    Water level is Same?

    B) The fisherman lowers the anchor and it hangs vertically, one foot above the bottom of the pond.

    Water level is Same?

    C) The fisherman lowers himself in the water and floats on his back

    Water level is Same?

    D) The nephew pops the balloon.

    Water level is Same?

    E) The nephew gets in the water and loses his grip on the string, letting the balloon escape upwards.

    Water level is Same?

    F) The fisherman knocks the tackle box overboard and it sinks to the bottom

    Water level Falls?
     
    Last edited: May 11, 2005
  11. May 11, 2005 #10

    Q_Goest

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    Science Advisor
    Homework Helper
    Gold Member

    These are essentially identical. Imagine the balloon being very large, to the point it's almost lifting the boat out of the water. In that case, it becomes obvious that the balloon is reducing the weight of the boat and thereby the water displaced, so when popped, the boat sinks a bit into the water and the level rises. Same holds true of the smaller balloon. Pop the balloon and the level rises.

    Your other answers are good Hotmail.
     
  12. May 11, 2005 #11

    OlderDan

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    Science Advisor
    Homework Helper

    You need to define what you mean by water level. It has to be measured relative to something. If it is the level of water relative to the boat it is a completely different problem than if it is being measured relative to something independent of the boat.
     
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