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Homework Help: Can someone please help me on an equilibrium problem?

  1. Dec 15, 2011 #1
    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. jcsd
  3. Dec 15, 2011 #2
    Re: Static equilibrium problem dealing with two concurrent forces

    Use the principle of deficiencies.
  4. Dec 15, 2011 #3
    Re: Static equilibrium problem dealing with two concurrent forces

    what is that?
  5. Dec 15, 2011 #4
  6. Dec 15, 2011 #5
    i probably sound really stupid saying this but.. is that calculus? because if it is i am currently only in algebra II
  7. Dec 15, 2011 #6
    No that's not calculus that sign (sigma) stands for the sum of all forces.
  8. Dec 15, 2011 #7
    okay thank you!
    i really appreciate it
  9. Dec 15, 2011 #8
    Did you learn how to use the principle of inertia?
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