NEED Help (Basically a Law of Cosines problem)

[Saladsamurai]

[SOLVED] NEED Help (Basically a Law of Cosines problem)

So in this problem, all I have to do is to solve it is find out by how much cables AC and AB elongate.

I thought I could just break it into two Right triangles and just use similar triangles (before and after elongation)

If you look at the upper right triangle, let's call it ACO, where O denotes the point on the wall halfway between C and B.

Then I tried doing,
$$\frac{AC}{OA}=\frac{AC'}{OA'}$$

$$\Rightarrow AC'=\frac{300}{300\cos30}*(300\cos30+2)$$

But this does not work. . . why the hell not??

My prof gave us the hint: "Use Law of Cosines to find the lengths of AC or AB after elongation"

How do I use Law of Cos if I don't know the angles after elongation, and moreover what is wrong with the process I tried?

I hate all of my classes. I miss physics.

Casey

 

[coffeebean51]

Mechanics of Materials eh?

http://www.mediafire.com/?0fmwmgeogi6

 

[Saladsamurai]

Where did you get that? Anyway, thanks! I think the dotted line should be labeled $L_{AC}'$ though. But now I see it. I never took a geometry course so this stuff makes me insane.

Do you know why my original method does not work?

 

[coffeebean51]

because they won't be similar triangles...

 

[Saladsamurai]

because they won't be similar triangles...

ummm. . . because the angle changes right?

 

[coffeebean51]

Yeah.

 

[Saladsamurai]

Short and to the point. I like your style beans

Welcome aboard,
Casey