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Force and coefficient of friction problem

  1. Oct 6, 2009 #1
    A initially stationary block of mass "m" is on the floor. A force of magnitude 0.500mg is then applied at upward angle 20 degrees. What is the magnitude of the acceleration of the block across the floor if coefficient of static friction = 0.6 and coefficient of kinetic friction = 0.5?

    i converted 0.5 mg into 5e-7 kg. so i drew a free body diagram and made the following equations: (F_N is the normal force)
    F_N + 5e-7(sin 20) = 9.8m
    5e-7(cos 20) - Fr = ma.

    so i solved for F_N and substituted into second equation:
    since Fr = F_N (coefficient of friction) but which coefficient of friction do i use in this scenario? also even if i do find which one to use, i can't eliminate m from the equation so how do i solve for a?
  2. jcsd
  3. Oct 6, 2009 #2


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    A force of magnitude 0.500*m*g is applied. Here m is the mass of the block.
  4. Oct 6, 2009 #3
    thank you! i can't believe i mistook mg for milligrams...
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