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Finding the kinetic friction between the block and surface

  1. Mar 19, 2015 #1
    1. The problem statement, all variables and given/known data

    The block shown is pulled across the horizontal surface at a constant speed by the force shown. If M = 5.0 kg, F = 14 N and Theta= 35°, what is the coefficient of kinetic friction between the block and the horizontal surface?

    2. Relevant equations

    Fx = Fcos(theta)
    Ff = Fn * Uk (Friction equation)
    F=ma
    Fn = mg

    3. The attempt at a solution

    I did it by myself and got 0.234, but the answer says it's 0.28. Can you explain this to me?

    My work:
    a = F / m
    a =( Fcos(35) - Fn * Uk ) / m= 0
    Fcos(35) / Fn = Uk
    14*cos(35) / (5 * 9.8) = 0.234 = Uk

    I don't know where I did wrong
     

    Attached Files:

  2. jcsd
  3. Mar 19, 2015 #2
    Nevermind! I got it! I forgot the Fsin(theta)
    It is
    Fcos(theta) - Uk(mg - Fsin(theta)) = 0
    14 * cos(35) / (5*9.8 - 14 sin(35)) = 0.28 = Uk
     
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