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Volume of Stone submerged in Water

  1. Jan 26, 2012 #1
    A submerged stone weighs 254N, but out of the water it weighs 1235N. The density of the water is 1000 kg per cubic meter. What is the volume of the stone?



    I understand that density=mass/volume but I don't know which numbers to plug in and I can't find help anywhere!!
     
  2. jcsd
  3. Jan 26, 2012 #2

    gneill

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    Why does the stone weigh less when it's submerged in water? What does the weight difference represent?
     
  4. Jan 26, 2012 #3
    Because of the buoyancy force??

    i took the difference between the weights which is 981N, divided it by 98.1 and got 10, then divided it by 1000 and got .01 is that right?
     
  5. Jan 26, 2012 #4

    gneill

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    Yes, that's correct.
    Why 98.1? What is 98.1?
     
  6. Jan 26, 2012 #5
    The force of gravity to convert it from newtons to kilogram
     
  7. Jan 26, 2012 #6

    gneill

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    The acceleration due to gravity is 9.81 m/s2.
     
  8. Jan 26, 2012 #7
    So should I not have used it as the conversion factor?
     
  9. Jan 26, 2012 #8

    gneill

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    Yes, you want to use the acceleration due to gravity in the conversion. But the value you employed was 10x to large. You used 98.1 rather than 9.81.
     
  10. Jan 26, 2012 #9
    Sorry that's what I meant
    So I on the right track?
     
  11. Jan 26, 2012 #10

    gneill

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    Yes, you're on the right track.

    Once you realized that the weight difference represents weight of the water displaced by the stone, you were on the right track to find the volume of the stone by finding the volume of that displaced water.
     
  12. Jan 26, 2012 #11
    so how do i use the volume of the displaced water to find the volume of the stone?
     
  13. Jan 26, 2012 #12

    gneill

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    Archimedes' principle of displacement -- the volume of water displaced by a submerged object is equal to the volume of the object...
     
  14. Jan 26, 2012 #13
    oh ok so .01 cubic meters is the answer?
     
  15. Jan 27, 2012 #14

    gneill

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    No, that's still off by a factor of 10. Did you fix your value of g?
     
  16. Jan 27, 2012 #15
    with that fixed the answer comes out to .1 cubic meters correct?
     
  17. Jan 27, 2012 #16

    gneill

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    That looks better :wink:
     
  18. Jan 27, 2012 #17
    haha ok thanks!!
     
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