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Homework Help: How to find Density/ Radius of planetesimals

  1. Nov 5, 2008 #1
    The ice rich planetesimals that formed the cores of the Jovian planets were about 10 times more massive than Earth. Assuming such an ice ball has a density of 2g cm g-3, what would its radius be? How does this compare to Earth's radius.


    I need Help =\
     
  2. jcsd
  3. Nov 5, 2008 #2

    Kurdt

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    What have you tried?
     
  4. Nov 5, 2008 #3
    I was thinking of multiplying the Earths mass by 10 then using the fomula m=dv

    and use the formula for volume of a sphere to get r? IDK
     
  5. Nov 5, 2008 #4

    Kurdt

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    Sounds like a good plan.
     
  6. Nov 5, 2008 #5
    okay so that would be m=dv


    10 x 5.97 x 1024 Kg which is 5.97x 1025Kg

    then convert from Kg to g 1kg= 1000g

    5.97x 1025Kg x 1000 g= 5.97x 1028g
    volume of a sphere= (4/3) pi r3

    5.97x 1028g= (2g cm-3)((4/3)pir3)

    im not to sure how to isolate R
     
  7. Nov 5, 2008 #6

    Kurdt

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    You just need a bit of algebraic manipulation. It might help if you use the letters instead of numbers right until the end.
     
  8. Nov 6, 2008 #7
    ok so it would be


    m=d 4/3 pi r3

    then m/ d(4/3)pi =r3 ?

    then r = cubed root of that anwser?
     
  9. Nov 6, 2008 #8

    Kurdt

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    Yes, that looks good.
     
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