Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

System of forces in equilibrium

  1. Nov 5, 2008 #1


    User Avatar

    A force [itex]F_1=i-3j-2k[/itex] at the point [itex]-2i+9j[/itex], another force [itex]F_2=2i+j-3k[/itex] at the point [itex]-i+yj-k[/itex] and a third force [itex]F_3[/itex] are equivalent to zero. Find [itex]y[/itex] for this to be possible. Find [itex]F_3[/itex] and its line of action in this case

    I infer that "equivalent to zero" means this system of forces is in equilibrium. I understand that for equilibrium, the resultant force on the system has to be zero, and the sum of moments must also be zero.

    I understand how to calculate moments ([itex]M=r \times F[/itex]), but fail to see how I can deduce [itex]y[/itex] without any information on where [itex]F_3[/itex] acts. I have [itex]F_3=-3i+2j+5k[/itex] by working out [itex]F_1+F_2+F_3=0[/itex] but am stuck beyond that.

    Any help would be appreciated.
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?