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Coefficient of Friction

  1. Dec 28, 2011 #1
    1. The problem statement, all variables and given/known data
    1.a block of mass 5kg moves on a rough horizontal plane with coefficient of friction (Dynamic) 0.2 under the action of a horizontal force of 30N. If the block starts from rest , find the distance it travels in the first 3 second.

    2.a particle of mass 6kg,moving at 8m/s on a smooth horizontal surface, goes onto a rough horizontal surface with a coefficient of friction 0.25> Find the distance it moves across the rough surface before coming to rest.

    3.This is my own question.Because I might get the concept of friction force wrongly
    It's been in my mind for about 3 days thinking of it

    A particle moving up a slope with a maintained speed of 1m/s
    In another situation a same particle moving up the same slope with a maintained speed of 5m/s

    Do the two particle use the same force?

    As the Coefficient,mass,gravity,angle of slope are the same


    2. Relevant equations
    F/N =u(Mew)
    F=ma
    s=ut+1/2 at^2

    Anyhow Regarding the equation,
    Relating The Momentum and Force
    F=ma
    F=m x v/t
    Ft=mv

    So If The Force is 15N and the object moving at a constant velocity last for 3 seconds
    Ft=mv
    15(3) = MV
    It will be 45 kg m/s ??




    3. The attempt at a solution
    1.
    M=5kg
    Force=30N
    ╬╝Dynamic = 0.2
    ╬╝Static = F/N (Force Used To Overcome the Static Friction)/(Normal Force)
    = 30/(30x9.8)
    = 0.1020
    Initial Velocity=0
    Final Velocity = 0
    Time=3 seconds
    Distance = Unknown

    Untill This Step
    What Should I Do With the two different coefficient of friction??

    2.
    Upon This Stage I Do Realize that I'm Getting Stupiddd
     
  2. jcsd
  3. Dec 28, 2011 #2
    Static friction is not an issue in this problem. Sum the forces and proceed either by impulse momentum or by Newton's Second Law and velocity-acceleration equation.
     
  4. Dec 28, 2011 #3
    "A particle moving up a slope with a maintained speed of 1m/s
    In another situation a same particle moving up the same slope with a maintained speed of 5m/s

    Do the two particle use the same force?"

    Yes.
     
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