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Homework Help: Rolling and Slipping

  1. Mar 13, 2010 #1
    1. The problem statement, all variables and given/known data
    "A 0.18-kg billiard ball whose radius is 2.8 cm is given a sharp blow by a cue stick. The applied force is horizontal and the line of action of the force passes through the center of the ball. The speed of the ball just after the blow is 3.9 m/s and the coefficient of kinetic friction between the ball and the billiard table is 0.64."
    How long does the ball slide before it begins to roll without slipping?
    How far does it slide?
    What is its speed once it begins rolling without slipping?

    2. Relevant equations
    translational kinetic=(1/2)mv^2 Rotational kinetic = (1/2)Iω^2
    (when rotating without slipping) v=rω a=rα
    Force of friction = force normal * coefficient of friction
    Iα=r x F
    L= r x p = rmvsin θ (i'm not sure if that is useful yet)
    3. The attempt at a solution
    I know that it's losing kinetic energy to friction
    Force of friction*distance to point where it begins rotating
    so I know that after that amount of energy loss... v=rω a=rα will hold true
    but I don't know what to do with this...

    The net force should just be the force of friction right? so a= Ff/m
    so vf=vi+at

    I'm confused as to what to do with any of this... it seems like I'm missing something....

    I have (1/2)mVi^2=Ff*Δx+.7mVf^2 (added rotational and kinetic assuming that it is rotating)
    and that's about all I can do I rearranged somethings and got about .7 seconds for the time. . . but i'm pretty sure that is wrong...

    direction please?
  2. jcsd
  3. Mar 13, 2010 #2
    Hope you don't mind me bumping it (I'll compensate by adding some more ideas I have....I'm still working on it and failing haha)
    I was thinking about the point of contact...when it begins to roll without slippage, the velocity at that point is 0 right? but with slipping....the sum of the vectors is NOT 0....it's v translation+r(omega) right? could I just use the angular acceleration I have to fine when r(omega) = v?
  4. Mar 13, 2010 #3
    I solved my own problem =DDDD sorry guys...I'm stupid.... maybe next time when it's really hard you guys will be interested enough to help? haha
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