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Homework Help: Use conservation of energy, find out velocity, then find distance?

  1. Dec 27, 2007 #1
    1. Two railroad cars, each of mass 7650kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision?
    Here does the thermal energy mean like to find friction? I used the conservation of energy formula, but it didn't work out. I don't really know what thermal energy is.
    2. A ski starts from rest and slides down a 22 degrees incline 75 m long. If the snow is level at the foot of the incline and has coefficient of friction 0.09, how far will the ski travel along the level?
    Then, i think i also need to use conservation of energy, find out velocity, then find distance?

    Hope you can give me some hint, thank you.
  2. jcsd
  3. Dec 27, 2007 #2


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    1) All of the kinetic energy in the railroad cars went 'somewhere'. Ultimately, it went into thermal energy. Thermal energy is heat. 2) Yes, conservation of energy. Find the potential energy change and equate it to frictional force times distance. Note: frictional force is different on the incline than on the level slope. You don't need to find velocity. Those are hints. Now get started.
    Last edited: Dec 27, 2007
  4. Dec 28, 2007 #3
    but how do I find the thermal energy??
  5. Dec 28, 2007 #4


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    that is how to find it. All of the kinetic energy was converted into thermal(heat) energy.
    [itex]E_k=[/itex] ?
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