A 1 gram weight is moving at 1000 m/s Would a 2 gram weight need to move at 250 m/s or 500 m/s to have the same kinetic energy? I'm guessing 250 m/s. So would a 4 gram weight need to move at 125 m/s or 250 m/s to have the same kinetic energy? And what object (out of the 1, 2, and 4 gram weights) requires the least amount of energy to move at it's suggested m/s, or is it the same? I was reading about railguns (if you hadn't guessed by now) and I read somewhere (I never believe anything at face value) that a 0.5 gram weight was moved at some silly high speed (over 10 km/s) but because of it's weight, lacked momentum. Surely even a 0.5 gram needle type ammo moving at over 10 km/s would have no problem with momentum?