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Math Help - Some basic questions

  1. #1
    Senior Member Twig's Avatar
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    Some basic questions

    Hi!

    We know from physics that  E = P \cdot t , where E is the energy, P the power and t the time.

    If we have P=P(t) , that is, power as a function of time, we could integrate this expression from t_{1} \mbox{ to } t_{2} , and get the total energy.

    Here is where I am confused.
    Which is correct?

    dE=P\cdot dt

    dE=P'(t)\cdot dt

    Because usually, \frac{dy}{dx}=y'(x) . This looks like the second one.

    But i also makes sense to think about  dE as some "energy strip" , with height P and width dt.

    Kinda want this cleared out.

    Thx!
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by Twig View Post
    Hi!

    We know from physics that  E = P \cdot t , where E is the energy, P the power and t the time.

    If we have P=P(t) , that is, power as a function of time, we could integrate this expression from t_{1} \mbox{ to } t_{2} , and get the total energy.

    Here is where I am confused.
    Which is correct?

    dE=P\cdot dt

    dE=P'(t)\cdot dt

    Because usually, \frac{dy}{dx}=y'(x) . This looks like the second one.

    But i also makes sense to think about  dE as some "energy strip" , with height P and width dt.

    Kinda want this cleared out.

    Thx!
    dE/dt = E', not P'.

    dE = P \cdot dt is the correct expression.
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  3. #3
    Senior Member Twig's Avatar
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    Yes of course what was I thinking

    Thanks man!
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