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Homework Help: Forces and Unit Vectors

  1. Sep 21, 2008 #1
    1. The problem statement, all variables and given/known data
    Suppose that the 1 kg standard body accelerates at 3.40 m/s2 at 155° from the positive direction of the x axis, owing to two forces, one of which is F1 = (2.6 N)i + (4.8 N)j. What is the other force in unit-vector notation and as a magnitude and direction? i-component of the other force?

    2. Relevant equations


    3. The attempt at a solution

    First I tried to find the x-component of F2.

    F2,x = max - F1,x
    F2,x = (1)(3.4 cos155) - (2.6 cos 155)
    I got F2,x to be -0.725 N but thats not the correct answer

    For F2,y I did:
    F2,y = may - F1,y
    F2,y = (1)(3.4sin 155) - (4.8sin 155)
    But its also wrong. Any ideas on what Im doing wrong?
  2. jcsd
  3. Sep 21, 2008 #2


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    Homework Helper

    I would suggest you try converting the 3.4 to i, j notation.

    Now they give you one of the Forces F1 and the resulting force F3 (the 3.4N force), where

    F3 = F1 + F2

    What they are asking for is F2 which can be given by

    F2 = F3 +(- F1)
  4. Sep 21, 2008 #3
    Thank you. I got it right
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