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Efficiency of energy transformation on a slide

  1. Jan 18, 2017 #1
    1. The problem statement, all variables and given/known data
    Students used a speed gun to measure the final speed of slider at the bottom of the slide. They measure the height difference between the top and bottom of the slide to be 3.0 m.
    If the speed of a slider at the bottom of the slide is 5.0 m/s, what is the efficiency of the energy transformation?

    2. Relevant equations
    mgh1+1/2mv^2=mgh2+1/2mv^2
    efficiency=Eout/Ein x100

    3. The attempt at a solution
    the masses of :mgh1+1/2mv1^2=mgh2+1/2mv2^2 cancel out, so I'm left with
    gh1+1/2v^2=gh+1/2v^2
    3(9.8)+1/2v1^2=1/2(5)^2
    When I isolate v1^2, I get a negative number which wouldn't work because I can't get the square root of it to find v. But after finding v, what would I do?
     
  2. jcsd
  3. Jan 18, 2017 #2

    haruspex

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    That equation assumes no losses.
    The 5 in there is for the case where there are losses, so the equation does not apply.
     
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