Law of sine/cosines to find resultant force

1. Dec 18, 2007

Saladsamurai

1. The problem statement, all variables and given/known data
So I am using Law of sine/cosines to find resultant force R and its direction.

My teacher gave me a hint to decompose the 600 and 800 into x and y components...but I have done this and cannot see what it helps me to derive? Anyone else see it?

Casey

Also, I have drawn parellogram law

2. Dec 18, 2007

Saladsamurai

I just don't see the relationship here. It looks like the y components might add up to the y component of R...but I am not sure how to prove it or if that can even help me here.

3. Dec 18, 2007

Saladsamurai

I'm going postal as we speak....I just thought you should know.

4. Dec 18, 2007

stewartcs

5. Dec 18, 2007

Saladsamurai

So if A+B=R then $A_x+B_x=R_x$ and $A_y+B_y=R_y$ and $$R=\sqrt{(R_x^2+R_y^2)}$$

Is this what I just read?! If so I did this earlier and got the wrong answer...but most likly because of a stupid mistake.

Is this correct though?

6. Dec 18, 2007

stewartcs

When you add vectors graphically, which way must the be aligned? Tail to Tip. Otherwise, you will have a sign problem and add when you should subtract.

So,

Rx = Ax + Bx, but A (the 600 N vector) is tail to tail with the B vector, so what does this tell you?

7. Dec 18, 2007

Saladsamurai

So, since the x components are in opposite directions, I need to take one as negative....thanks stewartcs! I knew I was overlooking the obvious!

Casey

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