Electro tech help

Discussion in 'Homework Help' started by bthistle, Feb 12, 2008.

  1. bthistle

    Thread Starter New Member

    Feb 12, 2008
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    This has to do with efficiency
    A pumping station raises 1600 kilograms of water a distance of 5 meters. if it has an efficiency of 75%, how much energy would be required?

    this is on my assignment i am puzzled haha

    thanks
    bill
     
  2. bthistle

    Thread Starter New Member

    Feb 12, 2008
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    is it missing some givens? if i had the initial energy i could get somewhere, but it seems like this question is lacking some givens.
     
  3. bthistle

    Thread Starter New Member

    Feb 12, 2008
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    i would show a attempt but not sure where to start.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Work = Force * Distance. With 75% efficiency, multiply times 1.333.
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    I'm no physics expert, so I may be incorrect. I believe work requires knowledge of the force involved, which is unknown in this case. You are only given that the potential energy of the water is raised.

    PE = mgh

    PE = Energy (in Joules)
    m = mass (in kilograms)
    g = gravitational acceleration of the earth (~9.8 m/sec2)
    h = height above earth's surface (in meters)

    Then compensate for efficiency.

    Steve
     
  6. bthistle

    Thread Starter New Member

    Feb 12, 2008
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    so use PE = mgh and answer is in Joules per sec right?
    then convert to watts
    then use the formal for efficiency.
     
  7. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    No, I don't think so. You asked for the energy required, not the power. Watts is a unit of power.

    You would consider power if you wanted to lift that load's potential energy in a certain amount of time, then you can figure out what sort of mechanical power you would need to do this.

    Steve
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Power is the rate at which energy is converted from one form to another. In this case, conversion is from electrical energy to 75% mechanical energy + 25% waste heat.
     
  9. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Here, there is no rate of energy, there is just potential energy. For example, as an object is raised against gravity, its potential energy increases. It doesn't matter at what rate this is happening, since that is a matter of power.

    This is my understanding anyways.

    Steve
     
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