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Homework Help: Trying to figure out gravitational attraction between two objects.

  1. Mar 23, 2009 #1
    Trying to figure out the gravitational attraction between two objects using Newton's Law of Universal Gravity.Need to figure out what the force is.Here is a model.If anything is in ordinary parentheses then it is an exponent.

    F1=F2=[6.673x10(-11)N m(2) kg (-2)] -----

    Force is proportional to the product of the two masses{120,000}and inversely proportional to square of distance between two point masses.{4,000,000}

    Please help me figure out what F1 is,since F1 is equal to F2.

  2. jcsd
  3. Mar 23, 2009 #2


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    First thing you must do is ensure all your numbers are in the right units: kilograms & metres (since those are the units that G is in). I don't know what units your numnber are in now.

    F - the force between them - will be equal to your formula there.
  4. Mar 23, 2009 #3
    Okay.The two point masses are in KG.The distance is in metres.G is in Newtons.
  5. Mar 23, 2009 #4


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    So, what answer did you get?

    The formula you have listed will calculate "the force of attraction between two bodies". One force, not two. Not sure where the F1=F2= came from.
  6. Mar 23, 2009 #5
    I can't figure it out.Kind of new to the concept of using Newton's laws.Kind of new to physics.
  7. Mar 24, 2009 #6
    I would think F1 is force felt by object #1 and F2 is the force felt by object #2, and they are equal in magnitude, while opposite in direction.

    Simply multiply and divide and you are done.

    G x M1 X M2 / (R x R) = F1 = F2

    From your post we have:

    M1 = 400 KG
    M2 = 300 KG
    R = 2000 M

    And we know G.

    So, just do the math! There's no physics left to figure out.
  8. Mar 24, 2009 #7
    I don't have a calculator that can even REGISTER newtons,and our teacher took it away.:(What a meanie.
  9. Mar 24, 2009 #8
    My sister THINKS it is 0.030.
  10. Mar 24, 2009 #9
    Do you guys have a suggestion
    for a good, reliable computer calculator for free that can do what Molinaro said to do?
  11. Mar 24, 2009 #10
    @ DaveC,It is that they BOTH exert gravitational force.F1 is equal to F2,which is the other force.
  12. Mar 24, 2009 #11

    then menu > VIEW > SCIENTIFIC
  13. Mar 24, 2009 #12
    My sister didn't incorporate G.My head hurts.I'm only in 5th grade,you know.
  14. Mar 24, 2009 #13
    I think it's 0.6.Please help me.More.
  15. Mar 24, 2009 #14


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    You don't need a calculator that registers' Newtons...
    You're just doing math.
  16. Mar 24, 2009 #15


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    They do both exert a force. That formula will calculate the entire forfce between the two masses.
  17. Mar 24, 2009 #16
    Once again,I AM A FIFTH GRADER!
  18. Mar 24, 2009 #17


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    I'm sorry, I missed that.

    Have you learned exponents?
    6.67x10^-11 is equal to .0000000000667


    F = (.0000000000667)*400*300 / (2000^2)

    Masses of 300-400kg that a distance of 2km have an extremely small force of attraction.
    Your answer should be a very, very small number - about 11 zeros.
  19. Mar 24, 2009 #18


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    Staff: Mentor

    No, we didn't know that, until you mentioned it in this post. :uhh:
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