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This question arises due to a problem I'd been solving recently:

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The question was to find the average power supplied by the water over the six hour period.

Now I have read this post which distinguishes the average power from instantaneous power. What I found was that one averages power when there is some sort of "repetition" or that the power is varying with a time period. In this case, the water level is varying, so the depth of the water is varying with time. How should I further proceed with this insight?

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  • $\begingroup$ Do not confuse with the word 'average' and 'instantaneous'. In physics the word'instantaneous' involves use of differential calculus. 'Average' just means (of course in physics) that you have to use simple formulue. Hence you have to just find potential energy of the running water as per as data and divide it by time. You will find the average power from tidal energy. $\endgroup$ Apr 17, 2016 at 4:23

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When you are asked the average of power, we do not care about how the power is fluctuating over time. All that concerns us is the amount of power delivered over time, and then we divide by that time duration. Whereas when it's instantaneous, we have to be more careful. We have to know the rate at which power is being delivered. ( This is often calculated by the tangent of a graph)

The best way to demonstrate instantaneous and average is through kinematics.

If you cover 10 km in 2 hours, average velocity is (10/2 ), 5km/h. However this does not give you any idea about the instantaneous velocity at any point. For that, we need additional details such as a displacement time graph where instantaneous velocity can then be calculated through the gradient.

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    $\begingroup$ "the amount of power delivered over time" Energy you mean? $\endgroup$
    – DKNguyen
    Jul 17, 2021 at 2:24

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