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Homework Help: Physics - Help with Power

  1. Apr 12, 2005 #1

    Nx2

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    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
     
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  3. Apr 12, 2005 #2

    Gokul43201

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    You have :
    [tex]P = \frac {mgh}{t} = gh \cdot \frac {m}{t} [/tex]

    Does that help ?
     
  4. Apr 12, 2005 #3

    Nx2

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    ok... so... hmmm lol sorry i dont understand where that equation was derived from.... h is height right?
     
  5. Apr 12, 2005 #4

    Gokul43201

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    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 ?
     
  6. Apr 12, 2005 #5

    Nx2

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    sorry... yea... we never learned that b4.
     
  7. Apr 12, 2005 #6

    Gokul43201

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    I'm not sure what you mean by this. Do you now understand how to solve the problem, or don't you ?
     
  8. Apr 12, 2005 #7

    Nx2

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

    - Tu
     
  9. Apr 12, 2005 #8

    Nx2

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    yea i understand... thnx
     
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