Ive done this question but from the answers Im getting I can see that I am going wrong, but I dont know where. There are lots of different parts to this question, I will show them all, followed by my attempt at working them out.(adsbygoogle = window.adsbygoogle || []).push({});

A Harbour has an average water covered area of approx. 10km^2. On a particular day there is a 4m tide. Making clear any assumptions that you make calculate:

a) The excess volume of water in the harbour at high tide compared with low tide:

Here I didnt know whether I had to assume my own low tide? So I did and assumed that

low tide was 1.5m...if Im being stupid and thats wrong please let me know, so I worked

out

Volume of water at high tide = 10km x 4m = 10000m x 4m = 40,000m^3

Volume of water at low tide = 10km x 1.5m = 15,000m^3

Excess volume of water = 40,000 - 15,000 = 25,000m^3

b) The excess mass of water in the harbour at high tide compared with low tide:

Mass=density x volume = 1027 x 25,000 = 25,675,000 kg

c) The increase in potential energy of the water in the harbour

This is where my numbers start getting rediculously big, making me think I must have

gone wrong somewhere

Potential energy at low tide = mass x g x height = 15,405,000 x 9.8 x 1.5 = 226,453,500

Potential energy at high tide = 41,080,000 x 9.8 x 4 = 1,610,336,000

Increase = 1,610,336,000-226,453,500= 1,383,882,500 J

d) If all of this energy could be extracted by a generator, how much power could be

produced:

Because all my numbers before this step are so big, I dont even know where to start with

this question.

Please help me by telling me where and why I am going wrong with this, I realy cant work it out. Thanks alot

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# Homework Help: Question on volumes of water, excess mass, potential energy and power

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