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Homework Help: Density buoyancy question

  1. Mar 21, 2005 #1
    hi all, i'm completely stuck on this question ive got no idea how to tackle it, ive looked back at previous examples and i dont know how this fits in with what ive see before.
    heres the question

    a boat floating in fresh water displaces water weighing 35.6kn

    what is the weight of the water displaced if it were floating in salt water with a density of 1.10x10^3kg/m^3?

    just something that came to mid could you work it out by going

    (density of fresh water divided by water displaced)times(density of salt water)
  2. jcsd
  3. Mar 21, 2005 #2


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    Science Advisor

    Actually, it's much simpler than that! A boat (or other object) will sink down into water until it has displaced a weight of water equal to it's own weight (Archimede's principle). If the boat initially displaced 35.6 KN, then it weighs 35.6 KN and will displace that weight in ANY liquid.

    (If the problem had given the VOLUME of fresh water displaced and then asked for the volume of saltwater displaced, then you would have to take the density into account.)
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