Universal gravitation: mass of 2 objects

[mickellowery]

Homework Statement

Two objects attract each other with a gravitational magnitude 1.00x10^-8N when separated by 20.0cm. If the total mass of the two objects is 5.00kg what is the mass of each?

Homework Equations

F_g=G*m₁m₂/r²
G=6.673x10^-11Nm²/kg²
I'm not real sure how to go about this one since they don't say whether or not the two masses are equal. The answers turn out to not be equal which killed my idea of how to set this up. I was going to try making one of the masses 5/2 and solving for the other mass but this just gives me half of the total mass.

The Attempt at a Solution

 

[Doc Al]

If the mass of one of the objects was 'm', what would be the mass of the other?

 

[mickellowery]

Thats a great question Doc. Would it just be m/2? I'm not very sure.

 

[Doc Al]

Would it just be m/2? I'm not very sure.

No guessing. Figure it out. Hint: What's the total mass?

Here's how to look at it. You've already called the masses m₁ and m₂. That's perfectly fine. You already have one equation: Newton's law of gravity. But since you have two unknowns, you'll need a second equation. Hint: m₁ + m₂ = ??

 

[mickellowery]

Oh OK so then it would be m₁=5-m₂. Then I would sub in 5-m₂ for m₁

 

[Doc Al]

Yep. Then you'd solve for m₂ (and then for m₁).

 

[mickellowery]

Alrighty thanks much for helping a nearly lost cause in physics.