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Homework Help: Simple POWer question

  1. Nov 18, 2007 #1


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    Gold Member

    [SOLVED] simple POWer question

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

    The electric motor of a model train accelerates the train from rest to 0.620m/s in 21.0ms. Total mass of train 875g.

    Find the average power delivered to the train during the acceleration.

    2. Relevant equations

    [tex]P_{av}= W_{net}/ \Delta t [/tex]

    3. The attempt at a solution

    Well..I'm not sure if this is correct...

    [tex] W_{net} = K_f- K_i= \Delta K [/tex] ===> I think this is correct but not sure..

    using that..

    [tex]1/2 mv_f^2 - 1/2 mv_i^2 = 0 [/tex]

    vi= 0

    [tex] 1/2 mv_f^2= 0 [/tex]

    [tex]1/2(.875kg)(0.620m/s)^2 = .1682J[/tex]

    P= 0.1682J/ 0.021s= 8.01W====> this seems pretty small but then again it's a model train..is this correct or did I miss something?

    I need to know if the way I did the question was correct since they mention acceleration but I'm not sure how would I apply that if I need to at all.

    Thank you
  2. jcsd
  3. Nov 18, 2007 #2


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    Homework Helper

    That's right. You used energy conservation, so you don't need to compute the acceleration etc.
  4. Nov 18, 2007 #3


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    Oh..okay then Thanks Dick :smile:
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