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Homework Help: Velocity and Position with Friction

  1. Feb 13, 2015 #1
    1. The problem statement, all variables and given/known data
    A 27kg box is being pushed across the floor by a constant force [PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char68.png96,0,0[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char69.pngN. [Broken] The coefficient of kinetic friction for the table and box is 0.14. At t=6s the box is at location [PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char68.png7,6,7[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char69.pngm, [Broken] traveling with velocity [PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char68.png9.5,0,0[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmsy10/alpha/144/char69.pngm[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char3D.pngs. [Broken]

    What is its velocity at 8.6s?

    v[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char7E.png=[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmex10/alpha/144/char1C.png [Broken] 15.1736 m/s , 0 m/s , 0 m/s https://s3.lite.msu.edu/adm/jsMath/fonts/cmex10/alpha/144/char1D.png

    What is its position at 8.6s? (Hint: Because the time step is so large, make sure to use the average velocity for this prediction.)

    d[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char7E.png=[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmex10/alpha/144/char1C.png [Broken] , , https://s3.lite.msu.edu/adm/jsMath/fonts/cmex10/alpha/144/char1D.png

    2. Relevant equations

    Kinematic Equations
    Position Update Equations
    Friction Equations

    3. The attempt at a solution
    How I found velocity..
    Force of friction = .14*27*9.8 = 37.044
    acceleration = (96N - 37.044)/27 = 2.18m/s^2
    Final Velocity = Vi + 2.18(2.6) = 15.1736m/s
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Feb 13, 2015 #2


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    Staff: Mentor

    I didn't check your numbers, but it looks like you made a good start. Now how can you find the second answer? What is the kinematic equation for position as a funtion of acceleration and time?
    Last edited by a moderator: May 7, 2017
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