2D Equilibrium

1. Oct 24, 2008

Melawrghk

This is just a problem from my midterm, and I was wondering if I did it correctly

1. The problem statement, all variables and given/known data

Weight of block B is 15kN, weight of block A is 25kN. Find force P that has to be applied to keep the system in equilibrium in tension in the cable

2. Relevant equations
$$\sum$$Fx=0
$$\sum$$Fy=0

3. The attempt at a solution
So first I figured I'd draw a FBD around block B (FBD1 on the image). I also decided I would use a different axis (x' and y'). From this I was able to write the equilibrium equations:
$$\sum$$Fx=3T-15*cos(60)=0, from which T=2.5kN
(I also wrote the Fy equation, but I won't post it because it serves no real point)

Next, I drew a FBD around block A (FBD2 on the image). I used a different axis once again. And I got:
$$\sum$$Fx=-25*cos(60)+P(cos30)+2.5kN=0, from which P=11.55kN

Is that correct? It makes sense in my head, but then again that wouldn't be the first time my gut feeling is wrong.Thanks!

2. Oct 24, 2008

PhanthomJay

...but this time, your gut feeling is right.