Does anyone have an equation that -- given energy applied to a mass over a distance -- will give me an (ideal) final velocity of the mass? If I direct a gigajoule to accelerate a gram over a distance of a meter, I obviously get into real trouble with c using conventional equations. I've found equations that apply Lorentz -- but they seem to do it as an adjustment after a raw, conventional velocity has been obtained, using this final, conventional velocity to plug into Lorentz. That can't work in this case. I'm looking for a function Ve( joules, mass, distance ) that works for all non-negative parameter values, and takes relativity into account. Can you help? Thank you very much!