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Density = mass/volume

  1. Sep 4, 2008 #1
    1. The problem statement, all variables and given/known data
    The mass of the earth is 5.97 e 24 KG. If density = mass/volume, what would be the density of the earth in pounds/ft(3)

    2. Relevant equations


    3. The attempt at a solution
    5.97 e24 KG X 2.2 lbs x 1ft(3)/62.4lbs = 2.1 e23 ft(3)...


    I dont know what to do after this.
     
    Last edited: Sep 4, 2008
  2. jcsd
  3. Sep 4, 2008 #2
    The mass of the earth is 5.97 e 24 KG. If density = mass/volume, what would be the density of the earth in pounds/ft(3)

    5.97 e24 KG X 2.2 lbs x 1ft(3)/62.4lbs = 2.1 e23 ft(3)...


    I dont know what to do after this, or am I even on the right track?
     
  4. Sep 4, 2008 #3

    LowlyPion

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    Welcome to PF.

    What have they asked for?

    [tex]Density = \frac{POUNDS}{Feet^3}[/tex]

    You have converted mass to pounds?
    And then what?
    What are the other numbers?
     
  5. Sep 4, 2008 #4

    chroot

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    I have merged these two threads together. Please do not post the same question multiple times.

    - Warren
     
  6. Sep 4, 2008 #5
    Thank you, but all I got is[tex]{5.97 e ^3}KG[/tex]for a number.... They are asking for the density of the earth in pounds per cubed foot.
     
  7. Sep 4, 2008 #6

    Borek

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    I suppose that was aimed at converting kg to lbs. For that you conversion factor unit should be lbs/kg:

    5.97e24 kg * 2.2 lbs/kg = 2.2*5.97e24 kg*lbs/kg

    Note, how kg cancels out.
     
  8. Sep 4, 2008 #7
    Yes, sorry about not including the conversions in my OP..

    http://img293.imageshack.us/img293/4198/92845158ma2.png
     
  9. Sep 4, 2008 #8

    Borek

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    Conversion is OK, but then you start making tricks. What is the density definition? If you know the mass, what is the other property of the object that you need to calculate density?
     
  10. Sep 4, 2008 #9
    The other property would be volume, but I dont know how to get it with the given info..
     
  11. Sep 4, 2008 #10

    LowlyPion

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    What volume are you looking to find? Maybe you can find it elsewhere?
     
  12. Sep 4, 2008 #11

    chroot

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    Yes, you need the radius or diameter of the Earth, as well as its mass, to find its density. If those values are not given, then there is not enough information to answer the question -- unless, of course, you are expected to go look up the radius of the Earth yourself.

    - Warren
     
  13. Sep 4, 2008 #12
    Should I Just write, not enough info. on my paper? He didnt tell us to search for the radius.
     
  14. Sep 4, 2008 #13

    chroot

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    If he only gave you one number, and you need two, then yeah -- that's not enough information.

    - Warren
     
  15. Sep 4, 2008 #14

    LowlyPion

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    The radius is readily available.

    I'd look it up and finish the answer.

    It's not like he can grade you off for finishing what he didn't provide.

    At least you would have shown initiative.
     
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