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Energy/power A levels physics

  1. Feb 13, 2014 #1
    Relevant formula
    : p(out) / p (in) x 100 percent = efficiency
    My question
    ImageUploadedByPhysics Forums1392289217.339333.jpg

    My approach
    ImageUploadedByPhysics Forums1392289268.189639.jpg

    But the right answer is 650kW
     
  2. jcsd
  3. Feb 13, 2014 #2

    BvU

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    You use P = F x v but you write ##\rho## x Area x v3. Is that the same ?
     
  4. Feb 13, 2014 #3
    Yeah I understand that it is not exactly the same. But my problem is , I don't have the value for F and v . And the only formula I know for power is force x velocity. So I did it by using the values given to derive a unit which is the same as power. But I can't seem to get the right answer. and I'm not sure whether my approach is correct or not. Can you teach me the correct method?

    anyhow, thank you for taking your time to try to solve my question:)
     
  5. Feb 13, 2014 #4

    BvU

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    Yes I can. You know that power is energy / time ?
    How much energy does the wind bring in /time ?
     
  6. Feb 13, 2014 #5
    If that case, the wind energy is 1/2 m (10)*2 am I right? Problem is , I don't have the value of mass and time :(
     
  7. Feb 13, 2014 #6

    BvU

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    That is correct. And they give you the area and the wind speed.
     
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