# Supernova, energy in the expanding remnant? simple question cant

1. Apr 12, 2014

### rwooduk

... 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!

2. Apr 12, 2014

### Staff: Mentor

If the given answer is an energy density, the problem statement is wrong, incomplete or there is something else missing.

3. Apr 12, 2014

### rwooduk

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.