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Homework Help: Unit Vector Notation Addition

  1. Aug 28, 2011 #1
    1. The problem statement, all variables and given/known data

    Consider the following vectors:

    a = (5.0m) i + (2.0m) j
    b = (-14m) i + (6.0m)j

    Sum of a+b in unit vector notation?

    2. Relevant equations

    3. The attempt at a solution

    I'm not sure about this notation, all I know about adding vectors is graphically. Does (5.0m) i + (2.0m) j mean 5 meters in direction i and 2 in direction j?
  2. jcsd
  3. Aug 28, 2011 #2


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    Yes, conventionally, i, j, and k are dimensionless unit vectors pointing, respectively, in the +x, +y and +z directions.
  4. Aug 29, 2011 #3
    Alright, got it.

    Now I am asked for magnitude and direction of new vector. After adding these, I found magnitude to be 12.04 which is correct, but direction is stumping me.

    I used trig to get the angle 41.64 as the angle direction of the new vector, but I'm not sure I'm finding the correct angle. After placing the vectors head to tail, I found the angle between the hypotenuse and x-axis. Is this the wrong angle?

    Since it's pointing upwards and to the left, should I add 90* to my angle?
  5. Aug 29, 2011 #4


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    What convention are you going to use to report the angle of the resultant? A common convention is CCW from the +x axis.
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