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Homework Help: Find the time required to complete each cycle

  1. Dec 9, 2007 #1

    sun

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    1. The problem statement, all variables and given/known data


    A particular engine has a power output of 6.00 kW and an efficiency of 26.0%. Assume the engine expels 6000 J of energy in each cycle.

    (a) Find the energy absorbed in each cycle.
    (b) Find the time required to complete each cycle.

    P=W/delta t
    e=W/Q

    1kW=3.6x10^6J

    Because the engine is expelling 6000J, does this mean it is negative? I'm not quite sure how to approach this problem.
     
    Last edited: Dec 9, 2007
  2. jcsd
  3. Dec 9, 2007 #2

    gtn

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    I suspect that if you start with a unit analysis the solution will jump out.

    Gary
     
  4. Dec 9, 2007 #3

    sun

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    Things aren't that obvious to me :(.

    I came to the realization that 1kW=3.6x10^6J, so 6kW=2.16x10^7J.
     
  5. Dec 9, 2007 #4

    gtn

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    kW aren't directly convertable to J. 1J = 1W x 1s or one Joule equals one Watt-Second. What you have is the conversion of a kW-hr (kilowatt-hour) to a Joule.

    The Watt is a measure of power. The Joule a measure of energy. To move between power and energy time must be considered.

    Gary
     
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