Astronomy - speed of debris of supernova inner ring

[accountkiller]

Homework Statement

Compute the speed of debris seen hitting the inner ring of Supernova 1987A. Assume radius of inner ring is 0.7 light years.

Homework Equations

The Attempt at a Solution

I'm not quite sure where to start. I thought about just using kinetic energy = 0.5mv^2 because I can find the total energy released on Wikipedia (10^46 J), but what would I put for m? Then I realized that way, I'm not using the radius that they gave me, so it's probably wrong. So...

I'd appreciate any guidance!

 

[chemisttree]

Inner ring started traveling in 1987 and has reached a distance of 0.7 ly. You have time and distance. Can you calculate speed from that?

How about this problem... if it takes me an hour to travel 50 miles, how fast am I travelling?