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Work done and a motor problem

  1. Mar 10, 2014 #1
    hi! so I'm in secondary two, and so far in my syllabus we have covered up to work done. now this is my homework, and I'm not sure whether my answer is accurate, could you help me with this?



    (I haven't learned the equations yet)



    image.jpg
     
  2. jcsd
  3. Mar 10, 2014 #2

    BvU

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    Hello Warp, and welcome to PF. Please use the template: we are house trained not to provide assistance unlees you use the template, for good reasons. See the guidelines.

    In this case you get an encouragement question in return: suppose the train of cars pauses at the top for a night. The electricity is switched off. Where is the (electrical?) energy stored that gets converted into kinetic energy the next morning ?

    The physics is a little more instantaneous: you want to describe the happening as a two-step process, where two conversions take place, one after the other.
     
  4. Mar 10, 2014 #3
    oh my god I'm sorry for not following the rules but thank you for the question. does that mean i have to describe the motor? i am really confused
     
  5. Mar 10, 2014 #4

    BvU

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    In a way, yes. Not how it works internally, but what is does in a physics, mechanics sense: A motor converts electrical energy into mechanical energy. It does work dragging the train up from a certain level to a higher level in a certain time.
    Apparently there is some energy stored in height: if you drop a brick on a bottle you can crush it (and crushing requires energy). And a train at the top of the ramp can acquire kinetic energy from going down, whichever way it got at the top: if Popeye eats spinach and puts it there it will behave exactly the same as when the motor dragged it up there a millisecond or a day ago. So it's not spinach energy, nor electric energy once the train is at the top.

    And it's good you feel confused. Better confused and looking for understanding one way or another than certain and dead wrong.
     
  6. Mar 12, 2014 #5

    berkeman

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    Thread locked because of inappropriate username choice...
     
  7. Mar 13, 2014 #6

    adjacent

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    :rofl::rofl:

    berkeman,thread is not locked.?
     
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