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Hi again

  1. Sep 7, 2004 #1
    Hey guys, boggled again :confused: need some help. And by the way, thanks to everyone who helped out on the last question...much appreciated!

    Combine the following two vectors to find the resultant vector.

    Vector A = 7.4 units at 30 degrees and Vector B = 11.1 units at 120 degrees

    A. Resulant = 13.34 units ; angle = 86.3 degrees
    B. Resulant = 18.49 units; angle = 60.0 degrees
    C. Resulant = 17.89 units, angle = 48.1 degrees
    D. Resulant = 17.89 units; angle = 41.9 degrees

    the only thing I can figure is that using the Pythagoryn Therom is that 7.4 and 11.1 comes out to 13.34 but I cant figure the math on how to get the angle to match up. thats asuming that 13.34 is a correct figure

  2. jcsd
  3. Sep 7, 2004 #2
    Ok...using a vector calculator at http://hyperphysics.phy-astr.gsu.ed.../vect.html#vec7 [Broken] I figured out that "A" is the correct answer. So using the Pyth therom is the right way to start

    But I still dont know how to do the math on the angle.
    Last edited by a moderator: May 1, 2017
  4. Sep 7, 2004 #3


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    Find the x and y components of each vector, add them together to find the resultant vector and the ratio of the y to x components of the resultant vector is the tangent of the desired angle.
  5. Sep 7, 2004 #4


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    The trick with vectors is to see them as triangles. You draw the vectors out (in the correct direction! VERY important!) then put the x and y components on them to form a triangle.

    Then you start solving the triangles... add their x and ys respectively and recombine the summed values using pythagoras to get the resultant.
  6. Sep 7, 2004 #5
    sine Alpha=11.1/13.34=.832 giving Alpha=56.3degrees. Adding vector A's
    30degrees to Alpha gives the total angle of 86.3degrees

    Thanks again :blushing:
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