No problem.

Small housekeeping note something went wrong with your or Bill G original mathematics as 1 kg at 706,944.44 m/s doesn't equal 50MJ.

The conversion for Kinetic Energy at 100% efficiency is 1/2MV^2

50MJ = 1/2 x 1 Kg x V^2

simplifying

50x10E6 Joules = 0.5kg x V^2

V^2 = 100E6 m/sec

V = sqrt(100E6) m/sec

V = 10,000 m/sec

So 1 Kg at 10,000 m/s (36,000kmph or 22369.36mph) = 50MJ

Last edited by Orac; 12/23/15 12:56 AM.
I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.