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Special theory theory oe relativity

  1. Jan 12, 2010 #1
    will the same energy be liberated if electron and positron are annihilated in the moving train and on the railway platform
  2. jcsd
  3. Jan 12, 2010 #2


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    Hi, sharma_satdev -- Welcome to Physics Forums!

    You might want to use more descriptive titles when you start threads. This entire sub-forum is about relativity.

    Mass-energy is conserved in both frames. In the center of mass frame, there is less mass-energy initially, so there is also less mass-energy in the final state consisting of the two photons.

    Whether the difference between the two frames should be considered as a difference in energy "liberated" is a different issue. Say you're going to use the radiation to power a heat engine. Any process, such as the cycle of a heat engine, has to conserve momentum. Therefore if you consider such a process in a frame other than the c.m. frame, there is always some energy that you can't harvest, because it's locked up in the c.m. motion. In this sense, the amount of energy liberated is the same in both frames.
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