# This is an engineering statics question, I need help on trig

1. Sep 11, 2011

### GreenAce92

1. If cylinder E weighs 30lb and theta = 15 degrees, determine the weight of cylinder F

2. Sigma F = 0 (Statics question)

3. I have gotten my separate components but I don't know how to solve the equations this sounds really stupid since I'm in calc III and physics II but my brain is just crapping out on me.

I have attached a sketch of the problem
The only thing(s) that are given are the three angles, and one weight.

I am having a hard time figuring out how to solve these equations.

So far I have
Sum(x) = 0 = -Fab cos30 + Fbc cos15
Sum(y) = 0 = Fbc sin30 - 30 - Fab sin15

I even have the solutions on hibbeler however I want to learn how to solve these equations, its definitely a basic concept that I should know how to do, that is solving trig problems.

#### Attached Files:

• ###### problem representation.png
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2. Sep 11, 2011

### GunnaSix

Can you solve the first equation for $F_{ab}$ in terms of $F_{bc}$? Once you do that, you should be able to plug that into the second equation and solve for $F_{bc}$.

3. Sep 12, 2011

### GreenAce92

Even with opposite signs /components?
I will try
Thank you

Question:
For the FBD on knot B
Can I not use the properties of angles that are symmetrical about a line segment to assume that Fcb cos 15 = 30cos15?

Actually in the physical sense that's not correct seeing as there is another tension force on the other side of knot b.

#### Attached Files:

• ###### Problem,.png
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Last edited: Sep 12, 2011
4. Sep 12, 2011

### GreenAce92

I think I've got it, I just hit a dumb wall of "I can't do trig even though I'm in calc III"