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Homework Help: Energy and Power

  1. Jan 24, 2004 #1
    1) The 2nd Law of Thermodynamics states that, “Entropy always increases.” Your high school physics teacher claims that this can be interpreted as “Energy is always wasted,” but this seems to violate the 1st Law! How is this NOT a violation?

    2) A person pulls a toboggan for a distance of 35.0 m by pulling on a rope that makes an angle of 25.0° above the snow. The toboggan moves at a constant velocity. If the tension in the rope is
    94.0 N, how much work is done by friction?

    3) Your friend moves into an apartment at the beginning of a college semester. His weight is 685 N. His belongings weigh 915 N. How much work does the elevator do while lifting your friend and his belongings 15.2 m upwards at a constant velocity? How much work does the elevator do on your friend – without his belongings – on the downward trip, also at a constant velocity?
  2. jcsd
  3. Jan 24, 2004 #2


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    You have to recognise what is "waste". Waste is not a matter of the energy getting destroyed. Waste is a loss of useful energy, often as heat. All this means is that the effeciency of a process must be less than 100%.
  4. Jan 24, 2004 #3
    You should post this in the Homework help section.... and show how far you have got!
  5. Jan 25, 2004 #4


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    Science Advisor

    [tex]W = (35)(94)cos(25)[/tex]

    [tex]W_1 = (15.2)(685 + 915)[/tex]

    [tex]W_2 = (15.2)(685)[/tex]

    Are you sure you even looked at the problems before posting them?
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