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Change in Thermal Energy?

  1. Oct 30, 2011 #1
    1. The problem statement, all variables and given/known data
    In the diagram given, you pull upward on a rope that is attached to a cylinder on a vertical rod. Because the cylinder fits tightly on the rod, the cylinder slides along the rod with considerable friction. Your force does work (W = + 100 J) on the cylinder–rod–Earth system (Fig. 8-23b). An “energy statement” for the system is shown in the diagram: the kinetic energy K increases by 50 J, and the gravitational potential energy Ug increases by 20 J.
    2. Relevant equations

    3. The attempt at a solution
    As far as I know, thermal energy is q=mcdT, but none of those values are given here.
  2. jcsd
  3. Oct 30, 2011 #2

    Andrew Mason

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    q = mcΔT has no application here since you are not given the mass or the temperature change or the specific heat. You are supposed to determine the work done against friction by applying the principle of conservation of energy. If 70J of work are used to increase kinetic and potential energy, how much of the 100J of work is done against the friction force?

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