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(Urgent) Finding the angle between A and B. Using magnitudes and the sum of vectors

  1. Aug 31, 2012 #1
    1. The problem statement, all variables and given/known data

    Vectors A and B have equal magnitudes of 15.0. If the sum of A and B is the vector 4.55 j, determine the angle between A and B.


    3. The attempt at a solution

    I thought I know what I was doing but apparently not. Please help!
     
  2. jcsd
  3. Aug 31, 2012 #2
    Re: (Urgent) Finding the angle between A and B. Using magnitudes and the sum of vecto

    Try looking at

    [tex]({\bf A} + {\bf B})\bullet({\bf A} + {\bf B})[/tex]
     
    Last edited: Aug 31, 2012
  4. Aug 31, 2012 #3

    Simon Bridge

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    Re: (Urgent) Finding the angle between A and B. Using magnitudes and the sum of vecto

    It helps if you show how you have attempted it.

    Have you tried sketching two equal magnitude vectors with some arbitrary angle between them, then working out the equation for the magnitude of the sum as a function of the angle? (there is a simplification if you put the y axis along the resultant vector.)
     
    Last edited: Aug 31, 2012
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