Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: E=mc2 problem help

  1. May 6, 2007 #1
    the celebrated equation E=mc2 or m=E/c2 (c is the speed of light) tells us how much mass is loss, m, must be suffered by a nuclear reactor in order to generate a given amount of energy, E/ Which of the following statements is correct?

    a)The same equation, E=mc2 or m=E/c2, also tells us how much mass loss, m, must be suffered by a flashlight battery when the flashlight puts out a given amount of energy, E.

    b) The equation E=mc2 applies to nuclear energy in a reactor, but not to chemical energy in a battery.
  2. jcsd
  3. May 7, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Why would either be true? or Why would E=mc2 be true for a nuclear reaction, but not true for a chemical reaction. Nuclear reactions usually involved energies in the MeV range, while chemical reaction energies are in the eV range.
  4. May 7, 2007 #3

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Einstein developed E=mc^2 without knowing anything about the nucleus. His paper published in 1905 predated Rutherford's discovery of the nucleus by about six years. In his http://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf" [Broken], Einstein showed that any object emitting/absorbing light of energy L will lose/gain mass in the amount m = L/c^2. I think that should tell you the answer to the question.

    Last edited by a moderator: May 2, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook