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How much thermal energy is produced in this collision?

  1. Oct 31, 2006 #1
    I cannot get these two questions at all. Can someone teach me how to do these?

    A spring with k = 47 N/m hangs vertically next to a ruler. The end of the spring is next to the 15 cm mark on the ruler. If a 2.7 kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?

    Two railroad cars, each of mass 6500 kg and traveling 100 km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision?
  2. jcsd
  3. Oct 31, 2006 #2
    first question:
    Use Hook's law... F=kx
    where F is the force that's pulling on the spring, which is the weight of the body thats hanging at the end. so...

    (2.7)(9.81) = (47)(x)
    x = 0.564m = 56.4cm
    x is the distance the spring will stretch, so the end of the spring will end up at 15cm + 56.4cm = 71.4cm
  4. Oct 31, 2006 #3


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    Part deux: What is the initial kinetic energy of the cars combined? What is their final kinetic energy? Where did all that energy go??
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