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Homework Help: Vector addition help

  1. Feb 24, 2008 #1
    I got a problem on a homework but the wording is kind of confusing and i dont know how to place it down on paper in a way that i can solve it...thanks for all the help..it looks basic, I find the Problem in weather its B+C=7i+5j or B+C=C being b+(7i+5j)=C

    1: A vector, B, when added to the vector C=7i+5j yields a resultant vector which is in the positive y direction and has a magnitude equal to that of C. what is the magnitude of B?
  2. jcsd
  3. Feb 24, 2008 #2
    You know for sure that B = -7i + yj, how do you suppose you find what y should be? What is the magnitude of C? Do the two vectors look similar at all?
  4. Feb 24, 2008 #3
    So magnitude of (B + C) = sqrt(7^2+5^2)
    and the y component in A when added to C's y component has to be greater than 0.
  5. Feb 24, 2008 #4
    im gettin 7.9 on the value of B..is that correct?
    thanks for your help
  6. Feb 24, 2008 #5
    Oh, which vector is supposed to have the same magnitude as C? If vector B is supposed to have the same magnitude then it should be B = -5i + (what)j, but if the resultant vector, call it D, is supposed to have the same magnitude then you need B = -5i + (you find it)j. Your answer would not be right for either case.
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