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Homework Help: Potential and Kinetic energy and a sled

  1. Oct 25, 2004 #1
    A sled and rider with a combined mass of 50kg are at the top of a hill that is 15m above the level ground. The sled is given a push providing an initial kinetic energy at the top of the hill of 1600J.

    A: choosing a reference level at the bottom of the hill what is the potential energy of the sled and rider at the top of the hill?

    B: After the push what is the total mechanical energy of the sled and rider at the top of the hill?

    C: If friction is ignored what will be the kinetic energy of the sled and rider at the bottom of the hill?

    So far I have this..and I'm not sure if it's right.

    PE=mgh PE= (50kg)*(9.8m/sec squared)*(15m) = 7350J
    E=PE+KE 1600J+7350J = 8950J

    after that I'm not really sure. Any help is greatly appreciated!
  2. jcsd
  3. Oct 25, 2004 #2
    You know the total energy, and if no work is done (draw a free body diagram if you want to verify this)....then the energy in the beginning is equal to the energy at the end....

    You know the potential energy at the end (h = 0).....so all you have is one unknown (the velocity).
  4. Oct 25, 2004 #3
    So..if I take (2*KE)/m and take the square root that would be right?
  5. Oct 25, 2004 #4
    well, not KE (assuming you mean Kinetic Energy), but Total Energy....

    (2*Total Energy) \ m and take the square root
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