1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Newton Law Gravitation - Multiple choice question?

  1. Apr 16, 2012 #1
    Newton Law Gravitation - Multiple choice question??

    1. The problem statement, all variables and given/known data

    Newton’s law of gravitation can be applied to the Earth-Moon system. Which of the
    following statements is not correct?

    A The value of G at the surface of the Moon is the same as that at the surface
    of the Earth.
    B The gravitational force between the Earth and the Moon is proportional to the
    square of the separation of the Earth and the Moon.
    C The gravitational force between the Earth and the Moon is proportional to the
    mass of the Moon.
    D The orbital time of the Moon about the Earth is independent of the mass of
    the Moon

    2. Relevant equations
    3. The attempt at a solution

    Lets go through all the options:

    A: G is constant so option A is is not the answer
    B: F = GMm/r2 so option B is is not the answer
    C: using the same equation as above, option C is is not the answer
    D: T = 4∏2r3 /GM where M = mass of earth so option D is not the answer

    The answer turns out to be B. Why?
     
  2. jcsd
  3. Apr 16, 2012 #2
    Re: Newton Law Gravitation - Multiple choice question??

    oh of course its an inverse relationship
    SMACK!!!
     
  4. Apr 16, 2012 #3
    Re: Newton Law Gravitation - Multiple choice question??

    B. Note that since [itex]\displaystyle{g=\dfrac{G\cdot m\cdot M}{r^2}}[/itex], the force is proportional to the inverse of the square of the radius, or inversely proportional to the square of the radius.

    EDIT: Oops, a bit late. Never mind.
     
  5. Apr 16, 2012 #4
    Re: Newton Law Gravitation - Multiple choice question??

    cheers anyway :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook