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Stuck With Energy Changes!

  1. Jan 17, 2007 #1
    A model train has an electric motor to drive it. The current though the motor is controlled by a rheostat and when it is moving slowly the current is 0.5A and the voltage is 5V.

    Total Power = 6W
    Power Developed By Motor = 2.5W
    Power Absorbed By Controller = 3.5W

    Total Voltage = 12V
    Voltage Across Motor = 5V
    Voltage Across Controller = 7V

    Current = 0.5A

    Find the energy changes in:
    1. The controller
    2. The motor

    Circuit Diagram
    Below is my diagram sketch of the circuit. Just click the link to look at it. It is a little rough but it should help you to understand my circuit.

    Attached Files:

    Last edited: Jan 17, 2007
  2. jcsd
  3. Jan 17, 2007 #2


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    Staff: Mentor

    Moved to homework forum. Please be sure to post all homework questions in the homework forums, and show some of your work so that we can help you.

    "Find the energy changes in the motor and controller" when what happens? When the rheostat is changed to some other setting? And to calculate energy, you need some time period specified, since E = P * t.

    Can you please post the full Question, word-for-word?
  4. Jan 18, 2007 #3
    The question just says what is the energy change. The reason I am stuck is because it doesn't give me a time to work out energy. I know the formula EPT.
  5. Jan 18, 2007 #4


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    Staff: Mentor

    Sorry, that makes no sense to me. Any chance you can ask the prof or TA for clarification?
  6. Jan 18, 2007 #5
    Well I just worked out it means what the electrical energy changes to.
  7. Jan 18, 2007 #6


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    Science Advisor
    Homework Helper

    Are you asking what a resistor turns electrical energy into?
    Or what a motor does with electrical energy?
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