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Homework Help: Moving block Work Problem

  1. Oct 14, 2009 #1
    1. The problem statement, all variables and given/known data

    a 3kg block moves initially at 4 m/s at t=0 and slides on a horizontal surface... Find the magnitude of word that must be done on the block to bring it to rest

    2. Relevant equations
    I believe we must use the equation w=Fs

    3. The attempt at a solution

    I drew the free body diagram and figured that the we have to find the opposing force and the relative displacement. im having a hard time getting started with this problem. i know that [F]=[N][m] and =[m]
  2. jcsd
  3. Oct 14, 2009 #2


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    Homework Helper

    Work done is equal to the change in kinetic energy.
    What is the initial KE?
    What is the final KE?
  4. Oct 14, 2009 #3
    okay so i figured that the change in KE=.5 x m x (vf^2-vi^2)
    for this problem it would equal 24J
  5. Oct 14, 2009 #4


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    Homework Helper

    Yes. It is correct.
  6. Oct 14, 2009 #5
    There is an extention to the problem:

    A constant friction force of 2 Newtons is exerted on the block by the surface find the magnitude of acceleration of the block

    So I used F=ma where the force i used was 2 and the mass was 3 so id id

    2/3 to find the acceleration which is .66666 is this the right method to answering this question?
  7. Oct 14, 2009 #6
    nm i got the right answer thankyou!
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