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Wood Floating on Water

  1. Mar 1, 2009 #1
    1. The problem statement, all variables and given/known data

    A block of wood of uniform density floats so that exactly half of its volume is underwater. The density of water is 1000 kg/m3. What is the density of the block?

    2. Relevant equations



    3. The attempt at a solution

    I tried 500 kg/m3 divided by 1000 kg/m3
     
  2. jcsd
  3. Mar 1, 2009 #2

    Chi Meson

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    Why did you divide the density of the block by the density of water? What did that get you?
     
  4. Mar 1, 2009 #3
    I found that the density equation was Density=Mass/Volume.
     
  5. Mar 1, 2009 #4
    I think you use Archimedies ' principle for this= the buoyant force on an immersed object has the same magnitude as the weight of the fluid displaced by the object.
     
  6. Mar 2, 2009 #5
    so which equation would that be?
     
  7. Mar 2, 2009 #6

    Chi Meson

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    Density = m/V, but that is NOT what you did above. You divided the "density of the block of wood" over "the density of water." THAT is what (500 kg/m^3)/(1000 kg/m^3) is. First of all, what made you pick "500 kg/m^3" anyway? It's not given information. It is in fact the answer to the question, but it appears to be accidental. Again my question is, why did you make that division?
     
  8. Mar 2, 2009 #7
    I did this because it said half of its volume is underwater so therefore I assume it was 500. So then I did the division. I guess I over thought the question. More than what was needed.
     
  9. Mar 2, 2009 #8

    Chi Meson

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    You still might need to explain why a density that is half of water will be half-submerged. Find Archimedes' principle and read it aloud. You also should understand that the division you did is NOT the same as the formula you stated.
     
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