Physics - Help with Power

1. Apr 12, 2005

Nx2

Hi guys, I was doing some homework when I got stuck on this question I came upon. It goes as follows...

Water is being pumped up to a water tower, which is 92.0m high. The flow rate up to the top the tower is 75L/s and each litre of water has a mass of 1.00kg. what power is required to keep up this flow rate to the tower?

Ok, so I know the formula for power is P = W/t, so I changed W into F•d and now my equation is P = (F•d)/t. then I changed F into mg and got the equation P = (mg•d)/t.
Ok, now im not sure if what im doing is right but I don’t know where to go from here… they gave me velocity but I don’t know what to do with it. Like I subbed all my values in like the mass, gravity and distance but I don’t know what to do with the “75L/s and each litre is 1.00kg.”…. any help would be appreciated, thanks.

- Tu

2. Apr 12, 2005

Gokul43201

Staff Emeritus
You have :
$$P = \frac {mgh}{t} = gh \cdot \frac {m}{t}$$

Does that help ?

3. Apr 12, 2005

Nx2

ok... so... hmmm lol sorry i dont understand where that equation was derived from.... h is height right?

4. Apr 12, 2005

Gokul43201

Staff Emeritus
Yes, h is the height. I just wrote what you had written and re-arranged the terms to bring out the factor (m/t). m/t is mass per unit time. Do you not know the value of this ?

5. Apr 12, 2005

Nx2

sorry... yea... we never learned that b4.

6. Apr 12, 2005

Gokul43201

Staff Emeritus
I'm not sure what you mean by this. Do you now understand how to solve the problem, or don't you ?

7. Apr 12, 2005

Nx2

ooo... ok i tried it and i got the answer!... thnx alot i appreciate it. good help.

- Tu

8. Apr 12, 2005

Nx2

yea i understand... thnx