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Homework Help: Vector of forces problem

  1. Sep 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Two forces, 422 N at 21◦ (above horizontal) and 256 N at 31◦ (below horizontal) are
    applied to a car in an effort to accelerate it.

    Find the direction of the resultant force
    (in relation to forward, with counterclock-
    wise considered positive, with −180◦ < <
    Answer in units of ◦.

    2. Relevant equations

    3. The attempt at a solution
    I found the resultant from previous question.
    My resultant=613.711888 N
    My x component of R=+613.405769
    My y component of R=+19.3815275

    Arctan (y/x)=arctan (19.3815275/613.405769)=1.809749

    My teaching assistant told me that my angle should be negative, but both of my resultant vector components lie in quadrant one, so shouldn't my resulting angle be positive as well?
  2. jcsd
  3. Sep 18, 2010 #2
    Hi strag

    I got the same result as you. :smile:
  4. Sep 18, 2010 #3


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    Science Advisor
    Homework Helper
    Gold Member

    Yes, the resultant angle is 1.8 degrees above the positive x axis, in the first quadrant (ccw from the positive x axis). So that looks positive to me. (And to songoku:wink:).
  5. Sep 18, 2010 #4
    Nice I got the problem right. Thanks for cross-checking!
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