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Archimedes's Principle or something

  1. Nov 20, 2006 #1
    So, the original question asks for me to estimate the mass of each leg of a person whose body past the hips is covered by water. They give me the person's actual weight and the apparent weight as well as the specific gravity of the body.

    I understand w' = w - Fb, Fb = F2 - F1 where F = PA or pghA
    But other than that, I'm lost. Do I need to find the amount of fluid displaced by the body first and somehow relate that to the force exerted by the weight of the person?

    I'm just looking for someone to point me in the right direction...
  2. jcsd
  3. Nov 20, 2006 #2


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    It seems there is something you are not telling us. Please state the whole problem.
  4. Nov 20, 2006 #3
    "A 78-kg person has an apparent mass of 54 kg (because of buoyancy) when standing in water that comes up to his hips. Estimate the mass of each leg. Assume the body has SG = 1.0."
  5. Nov 20, 2006 #4


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    The missing ingredient was not knowing that the body above the hips was not in the water. You already said you know w and w' so you can find Fb. Fb is the weight of the water displaced by the legs. If their SG is 1.0, how does their weight compare to the weight of the displaced water?
  6. Nov 20, 2006 #5
    Oh wow...so since SG is 1.0, the weight of the 2 legs would be equal to the water displaced, right? So Fb = 24, and divided between the 2 legs would be 12 kg.

    That was a lot easier than I made it...thanks so much!
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