 #1
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Homework Statement:
 I have a hard time understanding rigidbody equilibrium problem, especially when it a system of several objects. Sorry for asking so much here, but my exam is coming up and I really want to make sure that I try to understand all the things that makes me confussed.
Relevant Equations:

##\sum F_x=0##
##\sum F_y=0##
##\sum \tau=0##
So here are two problems I have been working with lately:
I have solved both, so I don't need the help to find the answers. The thing that confusses me is which object one should choose to apply the equations above. When it comes to the first problem, we apply the equations to the pole, but why not the box? And in second problem, we apply them to the point where the three strings meet. I had to look at the solution to find out which object or point I should focus on. But I'm afraid it won't be obvious to me on the exam what object or point to pick. Does anyone have some tips?
I have solved both, so I don't need the help to find the answers. The thing that confusses me is which object one should choose to apply the equations above. When it comes to the first problem, we apply the equations to the pole, but why not the box? And in second problem, we apply them to the point where the three strings meet. I had to look at the solution to find out which object or point I should focus on. But I'm afraid it won't be obvious to me on the exam what object or point to pick. Does anyone have some tips?