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Conservation Of Energy Problem

  1. Nov 17, 2005 #1
    So this is the quaiton that i have problem w/:
    A 4kg bundle starts up a 30 degree incline with 128J of kinetic energy. How far willl it slide up the incline if the coefficient of kinetic friction between bundle and incline is 0.3?

    Because E_initial + Work = E_final and the Work done in the system in this problem is jsut the fricition force, so I have
    128 + [tex]\mu[/tex]F_f = 0
    128 - [tex]\mu[/tex]mg cos [tex]\theta[/tex] d = 0

    since that d is what we are looking for, rearranging this equation gives me:
    128 / ([tex]\mu[/tex]mg cos [tex]\theta[/tex]) = d

    and d = 12.6m

    however, the answer is 4.3m, did I mess up any steps above?
     
    Last edited: Nov 17, 2005
  2. jcsd
  3. Nov 18, 2005 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Don't forget that gravity also does work on the object. (Or, alternatively, make sure that energy includes both kinetic and gravitational PE.)
     
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