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Homework Help: Hydrostatics physics question

  1. Apr 9, 2008 #1
    1. The problem statement, all variables and given/known data
    A girl of mass 40 kg and volume of 40 liter wants to keep her head of volume 3 liter above water surface as she can't swim . how much air in Kg should she fill in her jacket??


    2. Relevant equations



    3. The attempt at a solution
    mass of girl (m) = 40 kg
    volume of girl (V) = 0.04 m^3(meter cube)
    density of girl (D) = m / V = 1000 kg/m^3
    volume of head (v') =0.003 m^3

    let the mass of air in kg be x then

    total mass of body = 40 + x
    mass of water displaced = 40 + x
    volume of water displaced = 1000(40 + x)
    then
    volume of immersion = V - v' = .04- .003 = .397

    therefore from principle of flotation
    volume of water displaced = volume of immersion of floating body
    40000 + 1000x = .397
    x=.397-40000 = -ve value





    is my method correct??? and as " density of body = density of water " will require extra air to float.
     
  2. jcsd
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