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Vector problem missing magnitude of two vectors

  1. Aug 31, 2016 #1
    1. The problem statement, all variables and given/known data
    Force A has a magnitude of 200 lb and points 35deg N of W. Force B points 40deg E of N. Force C points 30deg W of S. The resultant of the three forces has a magnitude of 260 lb and points 85deg S of W. Find the magnitude of forces B and C.

    2. Relevant equations

    3. The attempt at a solution
    So this is what I tried:
    -200cos35 + Bsin40 - Csin30 = -260cos85
    -163.8304 + Bsin40 - Csin30 = -22.6605
    Bsin40 - Csin30 = 141.1699

    200sin35 + Bcos40 - Ccos30 = -260sin85
    114.7153 + Bcos40 - Ccos30 = -259.0108
    Bcos40 - Ccos30 = -373.7261

    This is what I tried but I still can't find the magnitude of B and C. Should I use system of equations to find B and C? Am I even on the right track?
  2. jcsd
  3. Aug 31, 2016 #2


    Staff: Mentor

    Yes, although I didn't verify that your equations are correct.
    I copied these equations from your work above. There are two equations in two unknowns, so solving these equations simultaneously should give you values for B and C.
    -200cos35 + Bsin40 - Csin30 = -260cos85
    200sin35 + Bcos40 - Ccos30 = -260sin85
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