Homework Help: Universal gravitation previous exam problem

1. Apr 3, 2014

Mikecarlson

1. The problem statement, all variables and given/known data
I'm having trouble with this problem attached. Any help would be appreciated.

2. Relevant equations

3. The attempt at a solution

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2. Apr 3, 2014

Simon Bridge

You have the basic idea - but the r in the gravity equation is the separation between the two objects, not their distance from the origin.

So if one object is at x1=4m from the origin, and the other is at x2=6m, in the same direction, then how far apart are they?
if one is at x1=4m and the other at x2=x, in the same direction, then how far apart are they?

3. Apr 4, 2014

Mikecarlson

So, are you saying object 1 and two are not 4 units apart?

4. Apr 4, 2014

Mikecarlson

The answer key has an answer of 4.98M. I have tried a few different ways to get that answer and have yet to figure it out. can you tell me if that answer is actually correct?

Thanks

5. Apr 4, 2014

Simon Bridge

Objects 1 and 2 are 4 units apart - that that's not the only separation that counts.
What is the separation between object 3 and 2?

The secret is to write the whole thing out in symbolic form first - then simplify the equation.

6. Apr 4, 2014

BvU

There is something else to worry about: you write an expression for |F| which is correct, but then you work it out to |F|+|F|=0 and there is a little thing you missed there.

The numerical value you found somewhere is totally unimportant, but correct.