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Homework Help: (Simple) Vector Problemdon't see what I'm doing wrong

  1. Sep 8, 2008 #1
    (Simple) Vector Problem..don't see what I'm doing wrong!!

    1. The problem statement, all variables and given/known data

    If the vector B is added to vector C = 3.7 i + 4.9 j , the result is a vector in the positive direction of the y axis, with a magnitude equal to that of C. What is the magnitude of B?

    Here is what I did -

    Magnitude is r = sq rt of Ax^2 + Ay^2 components

    therefore, the magnitude of C is

    3.7^2 + 4.9^2, take sq rt = 6.14 = magnitude of C

    The question is for the magnitude of B. The resultant vector, according to the problem, has the same mag as C, so I would use the Pythagorean theorem =

    A^2 + b^2 = C^2

    6.14 ^2 + 6.14 ^2 = 75.3992, take sq rt = 8.68.

    However this answer is not correct. I do not see where I went wrong, please help. Thank you!
  2. jcsd
  3. Sep 8, 2008 #2
    Re: (Simple) Vector Problem..don't see what I'm doing wrong!!

    Your question is difficult to follow. From the statement of the problem, start by writing

    Bx i + By j + Cx i + Cy j = sqrt[ (Cx)^2 + (Cy)^2 ] j

    What's the next step?
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