Two massless bags contain identical bricks, each brick having a mass M . Initial

Question

Two massless bags contain identical bricks, each brick having a mass M . Initially, each bag contains four bricks, and the bags mutually exert a gravitational attraction F1 on each other. You now take two bricks from one bag and add them to the other bag, causing the bags to attract each other with a force F2.

What is the closest expression for F2 in terms of F1?
A. F2 =3/4F1.
B. F2 = 1/2F1.
C. F2= 1/4F1.
D. F2 = F1 because neither the total mass nor the distance between the bags has changed.

I am thinking it might be D, but I dont want to guess on the problem, can anyone help me with this and explain why, Im kind of lost :/

Explanation / Answer

Given Mass of the brick is M Initially each bag contains 4 bricks that is 4M Then the gravitational force exerted on each other is F1 = G(4M)(4M) /r^2 F1 = 16 GM^2 /r^2   -------1 -------------------------------------------------------- If 2M is added to another bag, then the gravitational force exerted on each other is F2 = G(2M)(6M) /r^2 F2 = 12GM^2/r^2   ----------2 ------------------------------------------------------ Divide eq1 by eq2 (F2 /F1) = [ (12GM^2/r^2) / (16 GM^2 /r^2  ) ] (F2 /F1) = 3/4 F2 = 3/4 F1 option A is correct

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