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Kinetic energy and work problem

  1. Jun 30, 2015 #1
    1. The problem statement, all variables and given/known data
    In the figure here, a block of ice slides down a frictionless ramp at angle θ=55.0 ˚ while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 54.0 N and is directed up the ramp. As the block slides down through distance d = 0.400 m along the ramp, its kinetic energy increases by 80.0 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

    http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/c07/fig_7_C.gif

    2. Relevant equations
    K=1/2 mv2, w=Fd, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math080.gif, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math082.gif

    3. The attempt at a solution
    The work done in the positive x dir is -21.6 because the box is sliding down, if the kinetic energy is 80J then 21.6J+80J=101.6J is the total. But this is not right.
    http://i1164.photobucket.com/albums/q562/falsovero/20150630_163254_zps9et5lfe6.jpg [Broken]
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Jun 30, 2015 #2

    SammyS

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    What is the correct answer?

    Read the question you're asked carefully.
    "How much greater would its kinetic energy have been if the rope had not been attached to the block?"​
     
    Last edited by a moderator: May 7, 2017
  4. Jun 30, 2015 #3
    its would be 101.6 - 80. would be the difference between the the work with the 54N and without?
     
  5. Jun 30, 2015 #4
    Read the question you're asked carefully.
    "How much greater would its kinetic energy have been if the rope had not been attached to the block?"​
    thanks i need to work on this, it gets me often.
     
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