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Find the magniture of the vector using the figure below

  1. Jan 15, 2012 #1
    1. The problem statement, all variables and given/known data

    Find the magnitude of the vector that is the sum of the three vectors , , and in the figure : figure is the link
    http://imageshack.us/photo/my-images/14/yf0134.jpg/




    2. Relevant equations



    3. The attempt at a solution

    What I did was obtain Ax=0 Bx=7.5

    Ay=-8.00 and B13

    My problem came when trying to get Cx and Cy.

    The way the vector is placed in the figure confuses me but I got Cy= 12sin(25)= -10.87 since it is on the negative side, and Cx= 12Cos25=-5.07.

    I then got the squareroot of Ax+Bx+Cx^2+Ay+By+Cy^2
    Did I create the triangle wrong? If so how can I make sure to not make this same mistake
     
  2. jcsd
  3. Jan 15, 2012 #2

    Simon Bridge

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    That looks OK to me...
    Haven't you got Cx and Cy the wrong way around though?
    After all C is longer in x than it is in y and you have Cy as the bigger.

    just a niggle, Cx is not 12Cos25
    ... you should have written Cx = -12Cos25 because that is what it is.
    (you can lose marks that way)

    You are used to the angle measured wrt the x axis ... in which case Cx=12Cos(205), which is the same.
     
  4. Jan 15, 2012 #3
    Thank you!
     
  5. Jan 15, 2012 #4

    Simon Bridge

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    No worries - you see all the other angles were wrt the y axis? so that angle in C was 115 degrees anticlockwise from the y axis. Then you can use the same formula you used for the others.

    You can always construct the kinds of angles that make the math easier for you.
     
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