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Homework Help: Is this question fair?

  1. Dec 14, 2012 #1
    1. The problem statement, all variables and given/known data

    It asks: Vector A has magnitude 2 and vector B has magnitude 3 with an angle between them equalling 0, 90 or 180. If the magnitude of A X B = 6, what angle/s must be between A and B?

    3. The attempt at a solution

    Knowing that the scalar product of the two vectors can also be considered a magnitude, I went with cos(0) or cos(180). But the answer is sin(90). I understand that that's what it would be if the question is asking for a vector product, but it didn't specify. I see how their answer is also right.

    Am I misunderstanding something here? Or is it just known that the magnitude of the product of two vectors is the magnitude of the vector product and not of the scalar product?
  2. jcsd
  3. Dec 14, 2012 #2
    If the angle between two vectors is 0° or 180°, their cross product is a zero vector. So the angle between A and B must be the third alternative offered, i.e. 90°.
  4. Dec 14, 2012 #3


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    The symbol X in the product generally denotes a vector product. So if the statement of the problem had the product written as ##A## X ##B## then you would normally assume a vector product. A scalar product is usually denoted with a dot: ##A\cdot B##
  5. Dec 14, 2012 #4
    Ahhhh, thank-you so much.
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