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Homework Help: The pushed box with kinetic friction and an inital speed

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A box is given a push so that it slides across the floor. How far will it go, given that the coefficient of kinetic friction is 0.25 and the push imparts an initial speed of 3.7 m/s?

    2. Relevant equations
    E is sigma
    EFy/m = ay
    -> Fn - mg = 0
    -> because ay = 0
    -> Fn = mg
    EFx/m = ax
    -> (Fa - uk*Fn)/m = ax
    -> (Fa - uk*m*g)/m = ax

    V^2 = Vo^2 - 2a(delta x)

    3. The attempt at a solution

    yo = 0
    y = ?
    Vox = 3.7 m/s
    Vx = 0
    t = ?

    I manipulated the equation so I could get ax... The end result was...

    ax = Fa / m - uk * g

    However, I do not know what Fa is nor do I know what m is.. This problem has me stumped and if anybody could direct me to the proper logic or correct my logic I would be really content/happy!

    I'm really unsure of how to do this type of problem. We were not given an example in class regarding a problem like this.
  2. jcsd
  3. Oct 21, 2008 #2

    I think you are making the situation too complicated. Problems can usually be solved EITHER by forces and accelerations OR by energy considerations.

    I think here you would be better off considering the initial kinetic energy and the work done against friction as the block slides.

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