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Newtons laws of universal gravitation

  1. Mar 18, 2014 #1
    1. The problem statement, all variables and given/known data
    its 3.8 x 10^8 from Earth's core to the lunar's core
    calculate the gravitational attraction exerted by earth on the moon

    2. Relevant equations
    ag = GM/ r^2
    G= 6.67 x 10^-11
    M of earth= 5.98 x 10^24 ... r= 6.37 x 10^6
    M of moon= 7.36 x 10^22 ... r= 1.74 X 10^6


    3. The attempt at a solution
    ag = ( 6.67 x 10^-11)( 7.36 x 10^22) / ( 6.37 x 10^6) ^2 = 0.12 N
    I'm not sure if i'm right or not, I am just really confused as to where I plug in the numbers
     
  2. jcsd
  3. Mar 18, 2014 #2

    Andrew Mason

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    When the question asks for the gravitational attraction it is asking for the force. You are calculating the acceleration (toward the centre of mass of the earth-moon system). The units would m/sec^2.

    Other than that your answer appears to be correct. Welcome to PF by the way!

    AM
     
  4. Mar 18, 2014 #3
    But how would I calculate the force? And thank you.
     
  5. Mar 18, 2014 #4

    SteamKing

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    What is Newton's Second Law of Motion?
     
  6. Mar 18, 2014 #5
    F=ma, ok i see now but what mass would i use?
     
    Last edited: Mar 19, 2014
  7. Mar 19, 2014 #6

    SteamKing

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    If you have calculated the acceleration of the moon caused by the earth, then you would use the mass of the ...?
     
  8. Mar 19, 2014 #7
    The Earth?
     
  9. Mar 19, 2014 #8

    SteamKing

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    Try again.
     
  10. Mar 19, 2014 #9
    The Moon.
     
  11. Mar 19, 2014 #10

    SteamKing

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    Good job.
     
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