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Equilibrium of three suspended blocks

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Phys121VIU
#1
Jan20-12, 12:23 PM
P: 17
1. The problem statement, all variables and given/known data

http://imageshack.us/photo/my-images/851/45009287.png/

The problem(s) are shown in the link, but I'm having trouble getting them started.

2. Relevant equations



3. The attempt at a solution

For 3-12:

I think what I need to do is find the tension force in the ropes leading from each block to point A. Then with those forces I find the Sum of the forces in X and Y

From there i think i know what to do, its just that i dont know how to find the force in each rope!

My attempt:

For block B, the force in the the rope to point A is sin∅/200lb. For block C, the force in the rope to point a is sin(30)/100 =50lb .

Is this correct so far?
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Doc Al
#2
Jan20-12, 12:35 PM
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Quote Quote by Phys121VIU View Post
For block B, the force in the the rope to point A is sin∅/200lb. For block C, the force in the rope to point a is sin(30)/100 =50lb .

Is this correct so far?
No. First things first. What's the tension in the rope connecting to B and the rope connecting to C? Hint: No calculation is required. (Consider the forces on B and C.) Then you can worry about the force components acting on point A.

Careful how you write things: don't confuse sin(30)/100 with 100*sin(30).
Phys121VIU
#3
Jan20-12, 04:02 PM
P: 17
Quote Quote by Doc Al View Post
What's the tension in the rope connecting to B and the rope connecting to C?
I got it figured out, I was definately over thinking it.

The tension in the ropes are equal to the weight of the blocks, so rope AB is 200lb and AC is 100lb.

Then I find the Sum of forces for X and Y and solve for the unknowns!

Thanks!


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