Equation manipulation question

[seanfrommemo]

Can someone please explain to me how to go about solving this question?
"Two identical masses, separated by a distance d, exert an attractive force on one another equal to F1. If the mass of each object is doubled, while the distance between them is halved, what is the ratio of the new attractive force F2 to F1?

A) 1
B) 4
C) 8
D) 16"

The answer is supposed to be 16. When I try and divide them out, everything comes out to a ratio of one.

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[mysturi0us]

The equation for attractive forces is F=(k*m1*m2)/r^2. So when you increase both masses by two and halving the distance the equation would be F=(k*2*m1*2*m2)/(0.5^2)*r^2. Simplifying the equation would get you F=(k*4*m1*m2)/(0.25) r^2. So now take out all the variables out, because the actual variables did not change between the two forces. You would get 4/0.25, which would get you an answer of 16. I hope you can follow through my explanation. If you're still confuse, you can msg me.

 

[HinduHammer]

Above explanation is correct, only thing you have to remember is to use gravitational force equation and not f=ma or anything else...top half increases by 4, bottom half decreases by 4 = 4 / (1/4) = 4 X4 = 16.