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2D or 3D vector problem?

  1. Sep 17, 2009 #1
    2D or 3D vector problem??

    1. The problem statement, all variables and given/known data
    Find the vector product of Vector A cross Vector B(expressed in unit vectors) of the two vectors. What is the magnitude of the vector product?


    2. Relevant equations
    Vector A= 5.00i + 2.00j
    Vector B= 3.00i - 1.00j



    3. The attempt at a solution

    I know how to get the dot product of the two, but how do I find the cross product??
     
  2. jcsd
  3. Sep 17, 2009 #2
    Re: 2D or 3D vector problem??

    This vector problem is 2D. You don't have a k component to represent the third dimension.

    The cross product can be evaluated by

    U x V = |U||V| * sin(angle between U and V)

    |U| this means the "magnitude of U".

    Hope that helps.

    Thanks
    Matt
     
  4. Sep 17, 2009 #3
    Re: 2D or 3D vector problem??

    The answer says -17.0k and 17.0. So shouldn't this mean it's a 3D problem? My teacher never taught me this in class and gave us 2 vector problems like this.
     
  5. Sep 17, 2009 #4
    Re: 2D or 3D vector problem??

    No this is not a 3D problem. Where could the third dimension come from? The answers are equal and opposite in magnitude, that doesn't mean there is a third dimension.

    What is your attempt at the solution? Can you find the magnitudes of the Vector A and Vector B?

    Thanks
    Matt
     
  6. Sep 17, 2009 #5
    Re: 2D or 3D vector problem??

    The magnitude of vector a is 5.38, vector b 3.16. I calculated the angle between the two to be 40.2 degrees. So I took ABsin(40.2) and got my answer is 11.0. The answer in the back says -17.0k, 17.0. I'm confused.. Is the book wrong or me?
     
  7. Sep 17, 2009 #6
    Re: 2D or 3D vector problem??

    Nevermind, I solved it.
     
  8. Sep 17, 2009 #7
    Re: 2D or 3D vector problem??

    Good then, hope I helped you out.

    Thanks
    Matt
     
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