# Energy question help

1. Mar 3, 2009

### tnutty

1. The problem statement, all variables and given/known data

A pumped-storage reservoir sits 140 m above its generating station and holds 8.0×109 kg of water. The power plant generates 305 MW of electric power while draining the reservoir over an 6.7 h period.
2. Relevant equations

???
3. The attempt at a solution??
??????

Last edited: Mar 3, 2009
2. Mar 3, 2009

Units?

3. Mar 3, 2009

### tnutty

I added units. I am so confused on how to slolve this, and this is due in about 10 minutes.

4. Mar 3, 2009

### Dick

And what's the question?

5. Mar 3, 2009

### tnutty

What fraction of the initial potential energy is lost to nonconservative forces (i.e., does not emerge as electricity)?

6. Mar 3, 2009

### lubuntu

I'm think that basically if didn't lose any energy the power generated by the water would be the graviational potential energy. So you know that and you know what was actually produced....

7. Mar 3, 2009

### tnutty

what? Sorry could not understand you.

Feel free to explain please. I have untill 11:59 for this question, and its the last one.

8. Mar 3, 2009

### lubuntu

You know what you started with and what you ended with... so what you lost is obviously the difference in those 2 quantities

9. Mar 3, 2009

### Dick

Gravitational potential energy. You know, that mgh thing?

10. Mar 3, 2009

### tnutty

I understand that stuff, Can you solve it out so i can see how you do it.

I have untill 11:59pm.

11. Mar 3, 2009

### lubuntu

Dude, this is really simple,we told you exactly what you need to calculate, if you can't do it you don't understand the concepts and don't deserve point for your assignment due in 5 minutes.

12. Mar 3, 2009

### Dick

It's good you understand it. Work out mgh. Work out power*time. Take a ratio. I don't think anyone is going to do it for you. Especially since you understand it. Do it!

13. Mar 3, 2009

### tnutty

wait a ratio of what?

14. Mar 3, 2009

### Dick

The exact question seems to be asking for (initial potential energy-produced energy)/initial potential energy. As I read the question. Since the top half of that ratio would be the amount lost to nonconservative forces.

Last edited: Mar 3, 2009
15. Mar 3, 2009

### Dick

We gave it a try, lubuntu. Maybe next time.

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