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Force and Kinetic Energy

  1. Feb 19, 2009 #1
    1. The problem statement, all variables and given/known data

    Josie and Charlotte push a 12-kg bag of playground sand for a sandbox on a frictionless, horizontal, wet polyvinyl surface with a constant, horizontal force for a distance of 6 m, starting from rest. If the final speed of the sand bag is 0.5 m/s, what is the magnitude of the force with which they pushed

    2. Relevant equations


    F=MA
    W=Fdelta(r)cos(theta)
    3. The attempt at a solution
    since cos0= 1 I thought it was 36 because W/6=F so w/6=12(.5) so how is W not 36. I'm obnviously forgetting a crucial step but dont understand where. Any help would be great, Thanks a lot.
     
  2. jcsd
  3. Feb 19, 2009 #2

    Delphi51

    User Avatar
    Homework Helper

    Looks like you are using the idea that the work done equals the kinetic energy acquired.
    That would be F*d = 1/2*m*v^2 and it should work well!

    In writing F = 12(.5), you are confusing acceleration (unknown) with velocity (.5).
     
  4. Feb 19, 2009 #3
    Alright thanks a lot that makes sense! :)
     
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