At which locations would both planets gravitational force pull on you ?

[laurenwings5]

Homework Statement

http://i1046.photobucket.com/albums/b465/laurenwings5/Picture1-1.jpg

Two planets with the same diameter are close to each other, as shown.
One planet has twice the mass as the other planet.
At which locations would both planets’
gravitational force pull on you in the same
direction? From among these four locations,
where would you stand so that the force of
gravity on you is a maximum; i.e., at which
point would you weigh the most?

1. A and B; D
2. C; A
3. D; D
4. B and C; C
5. B and C; D
6. None of these
7. A and D; A
8. B; D
9. A and D; D

Homework Equations

I have no idea. Please help :/

The Attempt at a Solution

I would think C and D, but that's not an answer choice, so what am I doing wrong?

 

[madmike159]

Well its easy to see just from looking.

But to prove it you will need to use the inverse square law which is

F = G [tex]\frac{Mm}{r^{2}}[/tex]

Where F is the force in Newtons (the bit you need to find)
G is Newtons gravitational constant (6.673x[tex]10^{-11}[/tex]
M and m are the two different masses in Kg
r is the distance from the center of gravity.

The distances between the points appears to be the same, so you can just say r, 2r etc.