# Gravitation problems

1. Oct 9, 2005

### 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.

2. Oct 9, 2005

### 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?

3. Oct 9, 2005

### jrd007

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

4. Oct 9, 2005

### jrd007

There is an equation m1 + m2 ?

5. Oct 9, 2005

### Physics Monkey

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

6. Oct 9, 2005

### jrd007

That the individual masses will add up to 4.0 kgs?

7. Oct 9, 2005

### Physics Monkey

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

8. Oct 9, 2005

### jrd007

By setting the equations equal to each other?

9. Oct 9, 2005

### jrd007

How can I solve for them>?

10. Oct 9, 2005

### 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.

11. Oct 10, 2005

### jrd007

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