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Homework Help: The Law of Conservation Problem! (Application)

  1. Jul 21, 2010 #1
    1.A large superball and a small superball are dropped from the same initial height H. Both balls bounce back up to a height h , which is just a bit less than H. If, however, the small superball is placed immediately above the large superball and both are dropped to the ground simultaneously from height H, the small superball rebounds to a height h␣ >>> H! Explain this in terms of the Conservation Laws.

    2. Conservation Laws

    3.The small ball lands above the large ball. It ‘meets’ the large ball on its rebound, and so is given energy and
    momentum by the large ball before it (the small ball) rebounds off the large ball and reverses its own direction.

    I can only solve it partly.. Can someone please explain this and the answer?
  2. jcsd
  3. Jul 22, 2010 #2
    The large ball rebounds from the ground as before so it has energy enough to get to the original rebound height of 'H'.

    However, this time on the way up, it collides with the small ball, transferring some of it's energy to the small ball. (You can calculate exactly how much by treating it as a simple billiard ball collision with conservation of energy and momentum). Having lost that energy, it cannot bounce so high this time.

    The smaller ball, just before the collision has enough energy to bounce back to the height h but it now gains the energy transferred to it by collision with the big ball and so has enough energy to get higher than before. You can show how much higher by noting that the extra K.E. now becomes Potential Energy.
  4. Jul 22, 2010 #3
    ahh.. I get it now.. I was missing the key points of the Law of Conservation.. Thank you so much for your great help!! thank you..
  5. Jul 22, 2010 #4
    Y'r welcome :smile:
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