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Homework Help: Adding Vectors

  1. Mar 11, 2007 #1
    I JUST started adding vectors.. as in.. last class. I got a ton of questions, and have done three of them. The answers are given, but I got them wrong. I'll follow the little template already given:

    1. The problem statement, all variables and given/known data
    What is the net force on a stack of books which are applied two forces: 2.0 N 61 degrees N of W and 59 degrees N of E?

    The answer is 75.0 N, 73 degrees (N of E)

    2. Relevant equations

    3. The attempt at a solution

    http://img245.imageshack.us/img245/5965/vectorsao5.jpg [Broken]

    Thanks in advance!
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Mar 11, 2007 #2
    Have you heard of the parallelogram rule yet?
  4. Mar 11, 2007 #3
    Who in the what? :S

    I've never heard of that...

    My teacher just did one example on the board, we copied it down as fast as we could, and now I'm trying to do what I think she did...which is what I attempted.

    LOL I'm assuming I'm missing something obvious that I've never heard of before.


    edit: BTW, I'm in Grade 11 and have barley learned anything above the basics.
  5. Mar 11, 2007 #4
    Maybe that is for the resultant.

    Anyways, you can just put them head to tail(like I think you did)....and then solve them similar to how your find the hypotenuse on a right triangle.
  6. Mar 11, 2007 #5
    Thanks for the response, but I'm not quite sure what you mean... can you see what I did wrong?
  7. Mar 11, 2007 #6


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    Staff Emeritus
    Science Advisor

    Well, firstly, you're using x's and y's to mean different things on each diagram! Pick a coordinate system (the most conventional is that x components are horizontal, and y components are vertical) and stick to it!

    Now, the horizontal components are in opposite directions, so the resultant will be V2x-V1x.

    You seem to be close, so try again, this time sticking to a convention, and see how you do.
  8. Mar 11, 2007 #7

    Holy moly.... I haven't made that idiotic mistake since grade 8! And the first time I post a question like this on a forum, It's my lucky day and I do it for the first time in 3 years!

    Yes, thanks for pointing that out. I was able to get it.

    There's another 2 questions that have nothing to do with mixing up the x/y axis (lol), so they are still problems (I was hoping there was a solution to why all 3 were incorrect)


    Before posting any more problems, I'll go back and retry the other two to check for more embarrassing mistakes...

    This is comparable to last semester when I was frustrated with a single problem involving intersections of circles and lines in Math... only to have somebody point out that I had "1 x 1 = 2". LOL
    Last edited: Mar 11, 2007
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