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Friction down a slide

  1. Oct 7, 2007 #1
    A slide loving pig slides down a 40° incline (Fig. 6-24) in twice the time it would take to slide down a frictionless 40° incline. What is the coefficient of kinetic friction between the pig and the slide?

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    F=ma ; a=(V-Vo)/t ; F=m((V-Vo)/t)

    so m((V-Vo)/t) = m((V-Vo)/2t)F(friction)

    m cancels V-Vo cancels t cancels which leaves 1/2F(friction) = 1

    after solving for F(friction) I get 2, which is wrong, everything cancels pretty much. so I am at a loss
     
  2. jcsd
  3. Oct 7, 2007 #2

    Astronuc

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    Staff: Mentor

    One cannot assume (V-Vo) is the same. If the pig starts at rest Vo = 0. Simply using V / t or 2t doesn't work.

    Find the acceleration down the slide without friction, then find the acceleration with friction, and from that determine the coefficient of friction.
     
  4. Oct 7, 2007 #3
    Perhaps there is an easier way of doing this problem, but I did it recently and it's a heckofa lot more work than you have there. Here's a clue, this is about the coefficient of friction, and what do you multiply the coefficient of friction with to get friction? You need to start by drawing diagrams and figure out your forces, start calculating....
     
  5. Oct 7, 2007 #4
    how can I find either of these, all they gave me was the angle?
     
  6. Oct 7, 2007 #5
    Amazingly enough, you can do it. It's alot of chugging formulas, sines and cosines, solving for certain variables then substituting in other formulas etc. Start simply. Draw the picture of the frictionless slide, then figure out label the forces, split them into x and y, then do the calculations for those forces. You just have to calculate what you can, then keep looking to substitute. And be careful not to mix up sines, and cosines etc.
     
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