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Homework Help: Static Friction

  1. Mar 6, 2015 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    Fs = μ FN

    3. The attempt at a solution
    Ok, so I drew a free body diagram and tilted it 90 degrees so that Fg of the small box points right and Fstatic points left.

    Fg = 4.7 kg x 9.8m/s2 = 46 N

    we want Fs to equal 46 N , correct? so we use the formula

    Fs = (0.71) x FN

    FN being the force of big box on small box

    .71 x FN = 46 N

    FN = 64.8N

    Which is wrong. any help?
  2. jcsd
  3. Mar 6, 2015 #2


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    Homework Helper

    You calculated the normal force between the boxes, but you need the applied force, F.
  4. Mar 6, 2015 #3


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    Science Advisor

    What is the required acceleration of box one? How is the mass of box one relevant?
  5. Mar 6, 2015 #4
    oh, silly me.

    so the acceleration of the small box should be 64.8 / 4.7k which is 13.8 m/s^2

    we use F=ma , m being mass of both boxes together and a being 13.8 m/s^2

    F = 465 N
  6. Mar 6, 2015 #5


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