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Homework Help: Vector magnitude and direction question

  1. Sep 6, 2011 #1
    1. The problem statement, all variables and given/known data

    Suppose vector C = vector A + vector B where vector A has components vector A x = 4, vector A y = 2 and vector B has components vector B x = -3, vector B y = -5.
    (a) What are the x- and y- components of vector C ?

    I've solved this to figure out that x = 1 and y = -3 for C

    (b)What are the magnitude and direction of vector C ?
    magnitude I've solved this to be 3.2
    direction ? (clockwise from the x-axis) This is what I can't get. I've solved for the angle and gotten -72 degrees using tan -3/1. Does anybody know what I'm doing wrong?

    2. Relevant equations

    3. The attempt at a solution
    Last edited: Sep 6, 2011
  2. jcsd
  3. Sep 6, 2011 #2


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    Science Advisor

    Why do you say that answer is wrong. Perhaps you are not being accurate enough. 71 degrees, 35 minutes is slightly more accurate, 71 degrees, 34 minutes, and 36 seconds even more accurate. Or perhaps they want the answer in radians.
  4. Sep 6, 2011 #3
    It's an online problem that checks itself when you put in the answer. It's telling me that my answer of -72 degrees is wrong and I'm not sure why. Also, it wants it in degrees specifically.
  5. Sep 6, 2011 #4
    I've solved this to figure out that x = 1 and y = -3 for C

    If X is 1 then that would be east, and given that the Y component is negative, its south.

    I don't know the details of the question, but try East 72 South
  6. Sep 6, 2011 #5


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    Staff Emeritus
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    Homework Helper

    Perhaps they want an answer between 0 and 360 degrees.
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