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Homework Help: Newton's Law of Universal Gravitation

  1. Aug 9, 2010 #1
    1. The problem statement, all variables and given/known data
    I am doing a lab-"Kepler's Laws and Newton's Law of Universal Gravitation". There is an image representing various positions, at equal intervals, of a satelitte in an elliptical orbit around the earth. A list of planets and their radi and periods are given. I have calculated acceleration using two formulas a=GMm/r^2 and a=4pi^2r/T^2
    Question states: "Calculate acceleration using the two equations and compare the results. Do your results confirm Newton's law of universal gravitation?"

    2. Relevant equations

    3. The attempt at a solution
    Ex. of results: accleration obtained for Venus using 1st equation= 5.5407*10^24 and using 2nd equation=0.0113286
    I was expecting them to be the same...please help
  2. jcsd
  3. Aug 9, 2010 #2


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    Gold Member

    a=GMm/r^2 is wrong

    go back to the general equation

    m1=mass of Venus
    m2=mass of satellite



    compare to the one you originally had (a=GMm/r^2)
  4. Aug 13, 2010 #3
    But mass of the satellite isn't given..?
  5. Aug 13, 2010 #4
    Wait...so as you said to use a=Gm1/r^2...for venus I got a=(6.67*10^-11)(4.8690*10^24)/(1.08*10^11)^2= 2.784*10^-8
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