Law of sine/cosines to find resultant force

  • #1
Saladsamurai
3,019
6

Homework Statement


So I am using Law of sine/cosines to find resultant force R and its direction.

th_Photo3.jpg


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
 

Answers and Replies

  • #2
Saladsamurai
3,019
6
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
Saladsamurai
3,019
6
I'm going postal as we speak....I just thought you should know.
 
  • #5
Saladsamurai
3,019
6

So if A+B=R then [itex]A_x+B_x=R_x[/itex] and [itex]A_y+B_y=R_y[/itex] and [tex]R=\sqrt{(R_x^2+R_y^2)}[/tex]

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
stewartcs
Science Advisor
2,178
3
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
Saladsamurai
3,019
6
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?

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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