Gravitation: Find Masses for 2 Objects, 4 kg Total

[jrd007]

I know they involve F= G(m1 x m2)/r^2

1) Two objects attract one another gravitationally, with a force of 2.5 x 10^-10 N when they are .25 m apart. Their total mass is 4.0 kg. Find the individual masses.

 

[Physics Monkey]

You have a formula for the gravitational force. You know the force and distance between the two objects so you can find M_1 M_2, right? You also know what M_1 + M_2 is, right? Are these two equations enough to find M_1 and M_2?

 

[jrd007]

No... how can I find m1 and m2? Since there are two unknowns in it?

 

[jrd007]

There is an equation m1 + m2 ?

 

[Physics Monkey]

Yep, what does the statement "Their total mass is 4.0 kg" mean?

 

[jrd007]

That the individual masses will add up to 4.0 kgs?

 

[Physics Monkey]

Bingo! So now you know M_1 + M_2 and M_1 * M_2 and you can solve for both.

 

[jrd007]

By setting the equations equal to each other?

 

[jrd007]

How can I solve for them>?

 

[lightgrav]

With 2 equations and 2 unknowns, you have a choice ...
usually it is OK to solve the "simple one" for one unknown.
Substitute that expression into the "complicated equation",
and solve for the only remaining unknown.

Me, I'd solve the multiplication equation first, then
substitute one term into the addition equation.

 

[jrd007]

Thanks I did like you said, and then I used the Quadratic formula and got the answers!