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Homework Help: Resultant of multiple forces

  1. Feb 5, 2008 #1
    1. The problem statement, all variables and given/known data

    Two horizontal forces act on a 3.5 kg chopping block that can slide over a frictionless kitchen counter, which lies in an xy plane. One force is F1 = (3.1 N) + (7.8 N). Find the acceleration of the chopping block in unit-vector notation when the other force is (a) F2 = (-3.1 N) + (-7.8 N), (b) F2 = (-3.1 N) + (7.8 N), and (c) F2 = (3.1 N) + (-7.8 N).

    2. Relevant equations


    3. The attempt at a solution

    I feel like I want to add vectors but I do not know where the mass comes into play other than in the equation F=ma
  2. jcsd
  3. Feb 6, 2008 #2
    Go with your feeling!

    Use vector addition to get a single force on the board then use F = ma (more correctly the vector equation F = ma)
  4. Feb 6, 2008 #3
    So the resulting force for a would be 3.1-3.1 which is 0 and then 7.8-7.8 which is 0. so? the resultant force is 0i+0j. But how would i use this in the F=ma formula
  5. Feb 6, 2008 #4
    Rearrange as
    a = F / m
    then substitute your resultant force.
  6. Feb 7, 2008 #5


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    F = ma = mai + maj = 0i + 0j
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