1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Coefficient of kinetic friction of a sliding crate

  1. Jul 12, 2008 #1
    1. The problem statement, all variables and given/known data
    Ugonna stands at the top of an incline and pushes a 100 kg crate to get it started sliding down the incline. The crate slows to a halt after traveling 1.5m along the incline. The initial speed is 2.0 m/s and the angle of incline is 30 degrees. What is the coefficient of sliding friction?



    2. Relevant equations
    ΣF=ma
    ƒ = μN
    aΔx = ½(vf2 – vi2)



    3. The attempt at a solution
    I have my midterm on Tuesday and am working on problems at the end of the chapters. I am hoping that someone can confirm my work, to make sure everything is okay, or help me through it if anything is wrong. This is what I have.

    ΣFx = mgsinθ - ƒ
    ΣFy = mgcosθ +N = 0

    a = [(1/2)(0-2.0)2] / 1.5 m
    a = -1.3 m/s2



    Fy = mgcosθ +N = 0
    N = (100 kg)(9.8m/s2)cos(30)
    N = 848.7 N

    ΣFx = mgsinθ - ƒ
    Fx = (100 kg)(9.8m/s2)sin(30) - μN
    = (100 kg)(9.8m/s2)sin(30) - μ(848.7N)
    = 490 - μ(848.7N)


    ΣF = ma
    490 - μ(848.7N) = (100 kg)(-1.3 m/s2)
    - μ(848.7N) = -620
    μ = .73
     
  2. jcsd
  3. Jul 12, 2008 #2

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Seems okay to me!
     
  4. Jul 12, 2008 #3
    Awesome! Thank you!
     
  5. Jul 12, 2008 #4
    There is one thing; it looks just like a typo though:

    This:

    a = [(1/2)(0-2.0)2] / 1.5 m

    should be written like this:

    a = [(1/2)((0 m/s)^2-(2.0 m/s)^2)]/1.5 m

    The answer isn't changed, though.
     
  6. Jul 12, 2008 #5
    Ahh yes, definitely a typo; thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?