1. Dec 15, 2011

### darlingdarlin

i have my physics exam tomorrow and i need help understanding this problem because i got this wrong on a previous test
1. The problem statement, all variables and given/known data
Two concurrent forces are acting on a box with a mass of 50.0 kg. One force is 555 N acting at an angle of 140 degrees; the other force is 785 N at an angle of 200 degrees. What third force would have to be added to the situation to produce a state of equilibrium?

2. Relevant equations
f= ma i guess... i didnt use it though

3. The attempt at a solution
555sin(40)-785sin(20) >> V
-555cos(40)-785cos(20) >> H
then i square rooted V^2 + H^2
then i tan^-1(V/H)
and i got some negative funky number

Last edited: Dec 15, 2011
2. Dec 15, 2011

### mtayab1994

Re: Static equilibrium problem dealing with two concurrent forces

Use the principle of deficiencies.

3. Dec 15, 2011

### darlingdarlin

Re: Static equilibrium problem dealing with two concurrent forces

what is that?

4. Dec 15, 2011

### mtayab1994

$$\sum(F)=0$$

5. Dec 15, 2011

### darlingdarlin

i probably sound really stupid saying this but.. is that calculus? because if it is i am currently only in algebra II

6. Dec 15, 2011

### mtayab1994

No that's not calculus that sign (sigma) stands for the sum of all forces.

7. Dec 15, 2011

### darlingdarlin

okay thank you!
i really appreciate it

8. Dec 15, 2011

### mtayab1994

Did you learn how to use the principle of inertia?