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Homework Help: Energies - chemical and electrical (easy question)

  1. Feb 28, 2009 #1
    I have to graph changes in energies. And I have a question - so I have a battery that supplies power to a motor and some sensors. I have to assume it starts with 36000J of energy (chemical energy, right?). Then, pretend a motor uses 22J and shuts off. Now I would have 35978J of chemical left. But what about electrical? Is it the same as chemical in this case? Or is it equivalent to just the value of chemical used? So 22J...

    Also, I know the motor is 5% efficient. So if I know how much work it did on a certain item, would I have to multiply it by 20 to get the change in chemical energy?

    Thanks bunches :)
  2. jcsd
  3. Feb 28, 2009 #2


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    Supposing 100% efficiency, 22J of chemical energy are turned into 22J of electrical energy by the battery, then into 22J of mechanical energy by the motor.
    Yes, and 19 x 22J of chemical energy are turned into the same amount of thermal energy.
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