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Homework Help: Change in kinetic energy

  1. Oct 12, 2009 #1
    1. The problem statement, all variables and given/known data
    a block of ice slides down a frictionless ramp at angle Θ = 52.0° while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 52.0 N and is directed up the ramp. As the block slides through distance d = 0.8 m along the ramp, its kinetic energy increases by 82.0 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

    2. Relevant equations

    3. The attempt at a solution
    Here is what I have come up with so far. Now I may be totally wrong on this but I think that since this senerio is frictionless, if we set up a coordinate plane with the x axis = to Θ and FN-(mg)i=0 => FN=(mg)i
    and Wnet=Fr-(ma)jcos(0) we can treat this situation is if the fall was vertical.
    Based on this, It seems like the problem should be as simple as adding the energy lost by the tension to the given 82.0J. which would be Fdcos(180)= -41.6
    Here is where I'm getting screwed up because I think I'm setting something up backwards. I tried to reason it and plug in 123.6 for an answer but this is not correct either.
    what am I doing wrong?
  2. jcsd
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