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Work done by friction force

  1. Oct 30, 2011 #1
    1. The problem statement, all variables and given/known data
    A horizontal spring with spring constant 200 N/m is compressed 20 cm and used to launch a box across a rough horizontal surface. After traveling a distance it stops. What is the work done by friction force?

    2. Relevant equations
    [tex]W = F \cdot d[/tex]
    [tex]KE_{spring} = \frac{1}{2}k \Delta x^2 [/tex]

    3. The attempt at a solution
    I don't know where to start, because I'm not sure what other relevant equations I can use. I'm thinking that the friction has to do enough work to make the box stop (v = 0). But I don't know how to relate the work by friction to the energy of the spring.
     
    Last edited: Oct 30, 2011
  2. jcsd
  3. Oct 30, 2011 #2

    Delphi51

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    Initially you have the spring energy. It gets converted into kinetic energy. That gets converted into heat by the work of friction. All your initial energy is equal to the work of friction.
     
  4. Oct 30, 2011 #3
    Ah... so [tex]W_{friction} = KE_{spring} = \frac{1}{2}k \Delta x^2 = \frac{1}{2} \cdot 200 \cdot .2^2[/tex]?
     
    Last edited: Oct 30, 2011
  5. Oct 30, 2011 #4

    Delphi51

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    looks good!
     
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