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Homework Help: Vector homework question

  1. Jan 20, 2008 #1
    Hey everyone,

    So I'm completely stumped on this question and I have no clue on how to even start. Any help would be greatly appreciated.

    Vectors A and B have equal magnitudes of 23.0. If the sum of A and B is the vector 12.1 j, determine the angle between A and B.

    Thanks in advance.
  2. jcsd
  3. Jan 20, 2008 #2


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    Draw the resultant vector of magnitude 12.1N first, then draw the two vectors A and B that would give the resultant direction in the direction that you drew the 12.1N force in. Complete the parallelogram. Then use some trigonometry.
  4. Jan 21, 2008 #3

    Shooting Star

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    In this case, to save a lot of time, I would suggest the OP just use the formula for the magnitude of the resultant R of two forces P and Q, given by:

    R^2 = P^2 + Q^2 + 2PQcos(theta).

    The magnitude of R is given.
  5. Jan 21, 2008 #4
    Yeah I could agree, just use the law of cosines.
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