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Homework Help: Supernova, energy in the expanding remnant? simple question cant

  1. Apr 12, 2014 #1
    ... figure it out

    1. if a typical supernova ejects 2 solar masses of matter at a root mean speed of 7000km/s, how much energy is available in the expanding remnant?

    2. Relevant equations: unsure

    3. The attempt at a solution:

    E = 1/2 mv^2

    then divide by the volume, 4/3(pi)r^3

    do not get the correct answer of 6.52*10^-14 J/m^3

    the problem is i do not know how big the remnant is so if i find the total energy what do i divide by, there is no time given to work out the expansion, but lost with this one, any direction appreciated!

    thanks in advance
  2. jcsd
  3. Apr 12, 2014 #2


    User Avatar
    2017 Award

    Staff: Mentor

    The question asks about energy, not energy density.
    If the given answer is an energy density, the problem statement is wrong, incomplete or there is something else missing.
  4. Apr 12, 2014 #3
    thanks for the reply. that is the complete question and the answer provided, i was assuming (given the answer) that the question wanted energy per m^3, which as you state would be an energy density.

    i will ask my tutor for clarification of this and update this thread with an answer.

    thanks again.
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