# Homework Help: Inertial frame of reference help

1. Sep 16, 2006

### Kalie

In an inertial frame of reference, a series of experiments is conducted. In each experiment, two or three forces are applied to an object. The magnitudes of these forces are given. No other forces are acting on the object. In which cases may the object possibly remain at rest?

The forces applied are as follows:

2 N; 2 N
200 N; 200 N
200 N; 201 N
2 N; 2 N; 4 N
2 N; 2 N; 2 N
2 N; 2 N; 3 N
2 N; 2 N; 5 N
200 N; 200 N; 5 N

I figured that A and B and C were the only ones possible since the net force could add up to 0 but it says I'm wrong...
I think there is some conscept I am missing
help?

2. Sep 16, 2006

### neutrino

Can they add up to 0 in case C?

3. Sep 16, 2006

### Kalie

I thought so, but i tried a and b together and that was wrong too
...sorry I ment d

Last edited: Sep 16, 2006
4. Sep 16, 2006

### neutrino

There are actually 3 cases in which they can add up to 0. A and B are two, you need to find the third.

5. Sep 16, 2006

### Kalie

is it d? because that is what i tried and it was wrong

6. Sep 16, 2006

### neutrino

D should be right. A, B and D are the answers.

7. Sep 16, 2006

### Kalie

there is more than 3 it told me

8. Sep 16, 2006

### neutrino

I guess it could also work in E,F and H...the equal forces in those cases could act in certain direction for the resultant force to be equal to third force in each case.

Edit: I meant H, not G. Sorry.

Last edited: Sep 16, 2006
9. Sep 16, 2006

### Kalie

awesome it worked thank i should of thought about it acting on them from angles