I have to find the resultant of:(adsbygoogle = window.adsbygoogle || []).push({});

[PLAIN]http://img17.imageshack.us/img17/8263/68709011.jpg [Broken]

So I decided to break it up into components:

[PLAIN]http://img37.imageshack.us/img37/7032/71250823.jpg [Broken]

(The black arrow in the first picture is the blue arrow in the second, that's the way I did it!)

I found the blue line in the picture using the cosine rule:

[itex] c \ = \ \sqrt{30^2 \ + \ 40^2 \ - \ (2 \cdot 30 \ \cdot \ 40 \ \cdot \ \cos(120)) [/itex]

c = 60.827 and it's just horizontal along the x-axis.

Then I added c = 60.827 to the third vector:

[PLAIN]http://img96.imageshack.us/img96/1917/92586648.jpg [Broken]

I found the white arrow, the total resultant, using the same technique:

[itex] d \ = \ \sqrt{25^2 \ + \ 60.827^2 \ - \ (2 \cdot 25 \ \cdot \ 60.827 \ \cdot \ \cos(105)) [/itex]

d = 71.5

My book says the answer is 67.6

I got the angle of the resultant using the sine rule:

[itex] \theta \ = \ \sin^{-1} ( \frac{25 \cdot \sin(105)}{60.827} ) \ = \ 23.39 [/itex]

My book says the angle is: 11.3°

What did I do wrong?

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# Homework Help: What's wrong with this?

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