Newton Law Gravitation - Multiple choice question?

[jsmith613]

Newton Law Gravitation - Multiple choice question??

Homework Statement

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

Homework Equations

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?

 

[jsmith613]

oh of course its an inverse relationship
SMACK!

 

[Whovian]

B. Note that since $\displaystyle{g=\dfrac{G\cdot m\cdot M}{r^2}}$, 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.

 

[jsmith613]

B. Note that since $\displaystyle{g=\dfrac{G\cdot m\cdot M}{r^2}}$, 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.

cheers anyway :)