Efficiency of a water wheel

• Prozen1

  13 Apr 11, 12:42

  How would you do (b)(i) ?

  

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  I have gotten as far as calculating the PE stored in the water by first converting the volume to mass and the using mgh.

  Next, I multiply the PE as calculated above by the energy conversion ratio.

  This should give me the USEFUL Power output, correct ?

   

  Hence, Useful Power output - PE = power lost to friction.

  Using this method I get the WRONG answer. WHy ?