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Homework Help: Finding the Force

  1. Sep 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Two forces F1 and F2 are acting on a mass M=4kg. The force F1 = 11i + 5j + 7k, in N. The acceleration of the mass is given by a = 3i + 7j + 4k, in m/s2. Calculate the magnitude of F2 .

    2. Relevant equations
    F = ma

    3. The attempt at a solution
    Ok so what I tried here is doing F1 + F2 = ma
    so F2 = (ma)- F1

    I took a = 3i + 7j + 4k and multiplied all of the components by 4kg got 44i+20j+28k and then subtracted F1 = 11i + 5j + 7k and got 41i+13j+24k kg*m/s^2

    what do I do?
  2. jcsd
  3. Sep 18, 2009 #2


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    now subtract this from F1
  4. Sep 18, 2009 #3
    so i+23j+3k ? what units do I use for this? its saying im not using the right units. Isn't it N*m/s^2
  5. Sep 18, 2009 #4


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    'ma' is in N

    F1 is in N

    so if F2= ma - F1, then F2 is in N as well.
  6. Sep 18, 2009 #5
    cool I got it right it was 1i+23j+9k square the coeficents add them up and then square root to find the force N.
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