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Glass marble is dropped down an elevator shaft

  1. Nov 24, 2003 #1
    A glass marble is dropped down an elevator shaft and hits a thick glass plate on top of an elevatior that is descending at a speed of 2.0 m/s. The marble hits the glass plate 3.0 m below the point from which it was dropped. If the collision is elastic how high will the marble rise, relative to the point from which it was dropped?

    So far, I let the point of impact have potential energy = 0, which would make the top of the fall have a PE of 29.4m J. That would mean that the kinetic energy just before impact would be 29.4m = 0.5mv^2. Solving for v I got 7.7 m/s. All I need help with is figuring out the velocity just after impact, and I think I can take it from there. I thought it was just (7.7 - 2)m/s, but I'm not sure.
  2. jcsd
  3. Nov 24, 2003 #2


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    Re: Collision

    That's the velocity of the marble relative to the elevator after impact. Now find the velocity with repect to ground before finding the final height.
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