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Archimedes Principle Quick Question

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data
    In air, Bob's weight is 687 N. In water, it is 34.7 N.

    Determine Bob's average density.

    2. Relevant equations

    3. The attempt at a solution
    Is it correct to say that (buoyancy force) + 34.7 N = 687 N?

    If so then buoyancy force = (density of water)(volume)*9.81 m/s

    I can solve for the volume.

    Then I can use (density of Bob)(volume)(9.81 m/s) = 687 N do solve for Bob's average density.

    Is that right? I just want to make sure it's okay before doing the rest of the problem.
  2. jcsd
  3. Apr 18, 2010 #2


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    You are on the right track.
  4. Apr 18, 2010 #3
    I was just kind of confused because Bob isn't necessarily all under water. If he was half submerged, wouldn't that change things?

    I guess because the question doesn't specify, I should just assume Bob's entirely under water...
  5. Apr 18, 2010 #4


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    Yes, you should assume that. You cannot solve the problem otherwise, unless you know what percent of his volume is under water.
  6. Apr 18, 2010 #5
    Okay, thank you!
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