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Homework Help: Unit vectors

  1. Feb 12, 2008 #1
    1. The problem statement, all variables and given/known data
    Vector A=3i-1j and B=-i-4j
    Find vector A-B and|vector A-B|


    2. Relevant equations



    3. The attempt at a solution

    Vector A-B=4i-3j

    Is the |vector A-B|the magnitude or just the absolute value of the answer?

    Thank you very much
     
  2. jcsd
  3. Feb 12, 2008 #2

    ranger

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    |A| is the magnitude of a vector A. To avoid confusion, one can use ||A|| to denote magnitude.
     
  4. Feb 12, 2008 #3
    Thank you very much

    Is the other part correct? The magnitude is the same thing as the angle of the vector, right? Is there a formula for calculating the magnitude?

    Thank you
     
    Last edited: Feb 12, 2008
  5. Feb 12, 2008 #4

    ranger

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    The magnitude of a vector whose components are <a1, a2> (2 dimensional vector) is:

    [tex] \sqrt{a_1^2 + a_2^2}[/tex]
    Please do not confuse magnitude and direction. Although they are both characteristics of a vector, they are different things.

    Recheck A-B, the j component has its sign messed up.
     
  6. Feb 12, 2008 #5
    Thank you very much

    4i+5j does that look correct?
     
  7. Feb 12, 2008 #6

    ranger

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    Recheck.
    Let A = <a1, a2> and B = <b1, b2>

    A-B = <a1-b1, a2-b2>
     
  8. Feb 12, 2008 #7
    If vector A=3i-1j
    and B=-1i-4j

    in order to find A-B, don't you just do 3i--1i=4i and -1i--4j=3j

    Wouldn't it be 4i+3j?

    and is the magnitude of A-B 6.40?

    Thank you
     
    Last edited: Feb 12, 2008
  9. Feb 12, 2008 #8

    ranger

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    Yup :approve: 4i+3j is correct. You made the mistake of writing 4i-3j in your initial post.
     
  10. Feb 12, 2008 #9
    Thank you very much

    Regards
     
  11. Feb 12, 2008 #10

    ranger

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    But your magnitude doesnt look too good. Recheck that.
     
  12. Feb 12, 2008 #11
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