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Homework Help: Fluid Mechanics Density problems

  1. Oct 12, 2004 #1
    Is this correct?

    A 6-kg piece of metal displaces 1 liter of water when submerged. What is its density?
    Density = mass/volume 1 liter of water = 1000 cm3 = 1 kg
    Ans: 6 kg / 1000 cm3 = .006 cm3

    How would this one work out?
    When a 2.0-kg object is suspended in water, it ‘masses’ 1.5 kg. What is the density of the object?
    I'm guessing:
    Density = mass/volume = 2.0 kg/1.5 kg = 1.333
    Or 2.0 kg/ 1500 cm3 = .00133 cm3

    Now I'm totally lost on what to do:

    A vacationer floats lazily in the ocean with 90% of his body below the surface. The density of the ocean water is 1.025 kg/m3. What is the vacationer’s average density?
  2. jcsd
  3. Oct 13, 2004 #2


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    Science Advisor
    Homework Helper

    The buoyant force is equal to the weight of the water displaced (Archimedes principle). That allows you to do a force balance from which you can ultimately determine the volume of the swimmer!
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