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Mechanical Energy

  1. Jan 10, 2010 #1
    1. The problem statement, all variables and given/known data
    A 70.0 kg base runnner begins his slide into second base while moving at a speed of 4.0m/s. The coefficient of friction between his clothes and Earth is 0.70. He slides so that his speed is zero just as he reaches the base.

    A) How much mechanical energy is lost due to friction acting on the runner? ( i solved A already)

    B) How far does he slide?


    2. Relevant equations
    W=fdcos(0)


    3. The attempt at a solution
    I tried to take my answer from part A which was -560 J and have that equal the work, but im stuck
     
  2. jcsd
  3. Jan 10, 2010 #2

    rl.bhat

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    You have to find the frictional force.
    What is the equation for that?
     
  4. Jan 10, 2010 #3
    ff= ufn u= .70
     
  5. Jan 10, 2010 #4

    rl.bhat

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    Yes.
    Now W = ff*d*(cos180), because frictional force acts in the opposite direction of the motion.
     
  6. Jan 10, 2010 #5
    i don't have fn or the distance
     
  7. Jan 10, 2010 #6

    Matterwave

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    fn=mu*N

    then from W=fn*d you can get d.
     
  8. Jan 10, 2010 #7

    rl.bhat

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    fn = normal force = mg. You have already found W. Find d.
     
  9. Jan 10, 2010 #8
    what would N be?
     
  10. Jan 10, 2010 #9

    Matterwave

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    sorry, i had the wrong notation, I meant ff=mu*N and W=ff*d

    Here I'm using N as the normal force or fn.
     
  11. Jan 10, 2010 #10
    so ff x d x (cos180) = -560

    480.69 x d x cos 180= -560

    d= 1.16??
     
  12. Jan 10, 2010 #11

    Matterwave

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    looks good to me.
     
  13. Jan 10, 2010 #12

    rl.bhat

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    Your answer is correct.
     
  14. Jan 10, 2010 #13
    thank you for your help!
     
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