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Efficiency of a ramp

  1. Jul 25, 2016 #1
    1. The problem statement, all variables and given/known data
    A 7.0 kg box is pushed up the ramp (height is 6 m and hypo is 12 m) in 3.25 s. If it requires a force of 40 N to push at a constant velocity, what is the efficiency of the ramp?

    2. Relevant equations
    Eff=(Wout/Win) x100
    W= Fxd
    F=ma

    3. The attempt at a solution
    The problem I have is that I don't know if 40.0 N is the force for Wout or Win. But I am guessing that it is Win since it's the minimum force need to push at a constant velocity. Then to get Wout you find the Normal force of the box which is 7 kg x 9.8= 68.6 N then you use W=68.6 x 12= 823 J. 480/823=58% efficient. But of course that's not right.
     
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  3. Jul 25, 2016 #2

    Simon Bridge

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    How much energy goes into the box pushing it up the ramp?
    How much of that energy does the box finish up with?
     
  4. Jul 26, 2016 #3
    since it's a ramp, the normal force would not equal to the weight of object.
     
  5. Jul 26, 2016 #4
    So by definition the efficiency is eff=(how much energy you got out)/(how much energy you put in). In this problem, the 40N is the force you put in and the potential energy is the energy you get out. Hope that helps you
     
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