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Homework Help: Average frictional force.

  1. Sep 30, 2008 #1
    1. The problem statement, all variables and given/known data
    A 0.5 kg block is sliding across a table top with an inital velocity of 0.2 m/s. It slides to rest in a distance of 0.7m. Find the average friction force that retracted its motion.


    2. Relevant equations
    vavg= vf-vi, then d/vavg= t, then a=vavg/t, then fnet=m*a, bleh thats all i can really think to do now :S

    3. The attempt at a solution
    vavg= 0-0.2= -0.2
    t=d/vavg= .7/-.2= -3.5sec
    a= -0.2/-3.5=0.057
    fnet= 0.5*0.057=0.0287

    :S i have no ide ahow to find average frictional force from this :S
  2. jcsd
  3. Sep 30, 2008 #2


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    Homework Helper

    To figure the force you need to figure the deceleration. But you won't find it by using the Average Velocity.

    One relationship you can exploit is the Vf2 =Vi2 +2a*x
  4. Sep 30, 2008 #3
    but what would that help me get :S
  5. Sep 30, 2008 #4


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    Homework Helper

    You'd think if you had the negative acceleration you might be able to figure the Force that was retarding the block wouldn't you?
  6. Sep 30, 2008 #5
    i probalay would if i had any idea what i was doing. :(
    thanks anyways.
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