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Work and Energy

  1. Mar 6, 2016 #1
    1. The problem statement, all variables and given/known data
    A 35-kg child goes down a hill on a 5-kg sled. Starting from rest, she reaches a speed of 30 km/h at the bottom of the hill. The hill makes an angle of 25 degrees with the horizontal.

    (a) Assuming there is no heat generated by friction and air resistance, how high is the hill?

    I don't really know how to solve this problem, help, please?
  2. jcsd
  3. Mar 6, 2016 #2


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    Are you familiar with conservation of energy?
    What form of energy does the child have at the bottom of the hill? Where did this energy come from?
    Hint: In this case, the mass of the child and sled and the angle of the hill aren't required to find the answer (as long as you work symbolically and don't try to plug any numbers in until the very end, which is generally the best approach)
  4. Mar 6, 2016 #3
    I am familiar with COE and I think it has KE at the bottom of the hill...?
  5. Mar 6, 2016 #4


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    Correct. And do you know the formula for KE? What form of potential energy did the sled start with? Do you know the formula for that form of energy?
  6. Mar 6, 2016 #5
    would the whole formula be something like this: 0.5m(v)^2 = mgh?
  7. Mar 6, 2016 #6


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    Correct. Good work. Be sure to use the appropriate unit for velocity, a conversion in necessary.
  8. Mar 6, 2016 #7
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