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Homework Help: G=GM/r^2 gravity homework

  1. Dec 3, 2005 #1
    Hey!
    I need help for this problem.

    The mass of a hypothetical planet is 1/100 that the Earth and its radius is 1/4 that of the Earth. If a person weigths 150 lb on the earth, what would he weigth on his planet?

    I tried the formula g=GM/r^2 by doing a ratio but I do not find the right answer.

    Thank you
    B
     
  2. jcsd
  3. Dec 3, 2005 #2

    lightgrav

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    well, g = GM/r^2 , all right ...
    show me your actual work and I'll find your error.

    (I suspect that you forgot to square the ¼ ...)
     
  4. Dec 3, 2005 #3

    Pengwuino

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    What exactly did you do? It's not going to be a linear relationship...
     
  5. Dec 3, 2005 #4
    gp= GMp/Rp2
    gp= GMe/Re2
    ge/gp=(Me/Mp)*(Rp/Re)=100/4=25
     
  6. Dec 3, 2005 #5

    Pengwuino

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    Yup, you forgot to square the denominator. It's R^2 remember?
     
  7. Dec 3, 2005 #6

    lightgrav

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    yeah ... you know what that "2" is for ?

    If you're likely to forget the square (most people are), write the r^2 as r . r .
     
  8. Dec 3, 2005 #7
    OOPS!! thank you
     
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