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Homework Help: Two Forces Acting on an Object

  1. Jan 21, 2009 #1
    1. The problem statement, all variables and given/known data

    Two forces F1 and F2 are acting on a mass m=6.0 kg. The force F1 = 7.0i + 4.0j + 3.0k, in N. The acceleration of the mass is given by a = 2.0i + 7.0j + 4.0k, in m/s2. Calculate the magnitude of F2.

    2. Relevant equations


    3. The attempt at a solution


    Magnitude of F12=72+42+32
    Magnitude of F1=8.6 N

    Magnitude of a2=22+72+42
    Magnitude of a=8.31 m/s2


    shouldnt F2=(6.0 kg * 8.31 m/s2) - 8.6 N ?? (which is 41.24 N)

    The website where I submit my answer tells me that I am wrong please help me out.

  2. jcsd
  3. Jan 21, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This is good. Note that this is a vector equation. Use it to find the three components of F2, then find the magnitude.

    You can't just replace the vectors F and a with their magnitudes.
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