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Density calculation for a cork (less dense than water)

  1. Dec 7, 2007 #1

    ~christina~

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    Gold Member

    [SOLVED] density calculation for a cork (less dense than water)

    1. The problem statement, all variables and given/known data

    I was in lab and I had to calculate the density of a cork.
    I used a sinker and measured how much the sinker weighed in water.
    I measured how much the cork weighed in air. Then I tied the cork to the sinker and measured how much both weighed in water.

    Not sure how to calulate the specific gravity and density however.

    m1-m1= mo - mo'

    sp. gravity= mo/ (m1-m2) = density

    data:

    mass cork in air : 8e-4kg

    mass of cork and sinker with only sinker submerged: .11119kg

    mass of cork and sinker with both submerged : .108kg


    I was thinking that I'm not quite sure what the book means (notation wise)

    but

    sp gravity= 8e-4kg/ (.11119kg - .108kg) = density

    sp gravity= .2507

    density = .2507 g/cm^3

    the thing was that I'm not sure whether the m1-m2 is the
    m (sinker submerged)- m(sinker and cork submerged) because then it would be a positive value for density and that would technically be correct.

    The book seems to explain it's the other way around with the m (sinker and cork submerged)- m(sinker submerged) but then it would be negative so I'm confused on that.

    which way is correct?

    Thank You
     
  2. jcsd
  3. Dec 8, 2007 #2
    Densities are positive--you did it correctly. I'm pretty sure it's that way because the cork is relatively heavier in air than in water (it floats in water and not air) so subtracting the mass of the cork/sinker combination with the cork still in air minus the mass of the cork/sinker combination in water should be positive.
     
  4. Dec 8, 2007 #3

    ~christina~

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    Gold Member

    Thank you, that's what I thought.
     
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