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Vector addition help!

  1. Nov 25, 2011 #1
    1. The problem statement, all variables and given/known data
    Find the resultant for the following directions.
    20 degrees east of south for 1/2"
    80 degrees South of west for 5"
    15 degrees west of north for 1"
    35 degrees North of East for 3"
    40 degrees South of East for 1"


    2. Relevant equations
    R2 = a2 + b2



    3. The attempt at a solution

    i graphed the measurements with each 5" = 1/2" on graph paper. then i connected the tail of the first vector to the head of the end point and measured the resultant but when i calculated it i got 31.55, to calculate this i found the x,y for each vector. vector 1- 4.69,-1.71. vector 2- - and -8.68, -49.24. vector 3- -9.66, 2.59. vector 4- 24.57, 17.21, vector 5- 8.19, -5.74. i added up the totals for each x and y then used the resultant formula to get the resultant to be 31.55. is that correct?
     
    Last edited: Nov 25, 2011
  2. jcsd
  3. Nov 25, 2011 #2

    gneill

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    Staff: Mentor

    Show your calculations!
     
  4. Nov 25, 2011 #3
    i showed calculations can you help?
     
  5. Nov 25, 2011 #4

    gneill

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    Staff: Mentor

    31.55 was a value you measured on the graph paper, or was it a numerical calculation? Perhaps I'm not clear on what the point of the exercise is. Is the idea to find the resultant by graphical method or by numerical calculation? Or both???

    Can you pick a vector, say vector 1, and show how you found the x and y components?
     
  6. Nov 25, 2011 #5
    31.55 was found by calculations. i was asked to find both ways graphically and by calculator.
     
  7. Nov 25, 2011 #6
    i found the vectors x, y by plugging it in my calculator in an app
     
  8. Nov 25, 2011 #7

    gneill

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    Staff: Mentor

    Okay. I think your calculator app is giving you the x & y components in reverse order (or you're swapping them somehow), and they seem to be multiplied by 10.

    If we take a Cartesian coordinate system where y is North and x is East, then for the first vector the angle is 20° East of South, which is -90° + 20° = -70°. The components are

    x = (1/2)*cos(-70°) ; y = (1/2)*sin(-70°)

    x = 0.1710 ; y = -0.4698

    You should verify that your app gives you these results for the components of vector 1. After that, construct a table with the magnitude, angle, and components for each vector.
     
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