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Kinectic Energy Question

  1. Oct 17, 2006 #1
    A wrecking ball, with mass of 315kg, hangs from a crane on 10.0m of cable. If the crane swings the wrecking ball so that the angle that the cable makes with the vertical is 30.0º, what is the potential energy of the ball in relation to its lowest positio? What will be the kinetic energy of the wrecking ball when it falls back to the vertical position? What will be the speed of the wrecking ball?

    I have no problem finiding the potential energy, but I don't know how to calculate the kinetic energy. and i know EK = ½ mv², but i dont know how to use it here. What should I do?
  2. jcsd
  3. Oct 17, 2006 #2


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    In the system as you describe it, there is no loss of energy, so any potential energy is going to be converted completely into kinetic energy.
    In other words, KE = PE!
  4. Oct 17, 2006 #3
    Thanx alot
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