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Homework Help: Determining Coefficient of Kinetic Friction w/m, t, and v

  1. Mar 21, 2015 #1
    1. The problem statement, all variables and given/known data
    A 2.0 kg block of wood slides over a horizontal surface and comes to rest in 2.5 s. If its initial velocity was 9.0 m/s, what is the coefficient of kinetic friction?

    2. Relevant equations
    change in rho=F*change in t
    Force of friction = mu*Force normal
    Force normal=mg

    3. The attempt at a solution
    rho=(2.0 kg)(9.0 m/s)=18 kg*m/s
    18 kg*m/s=Force of friction(2.5 s)
    Force of friction=7.2
    mu*Force normal=7.2
    mu(2.0 kg)(9.80 m/s squared)=7.2

    I don't know what the correct answer to this question is and I potentially may not know until the day of my exam. Can anyone tell me if I'm doing this correctly or if I'm missing something? I really appreciated it!
  2. jcsd
  3. Mar 21, 2015 #2


    User Avatar

    Staff: Mentor

    Looks good to me.

    F = ma = μN = μmg

    a = μg

    μ = a/g = [(9m/s)/(2.5s)]/(9.8m/s^2) = 0.367

  4. Mar 26, 2015 #3
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