I believe you&#x27;ve misunderstood his English.  If it takes 1 Joule to accelerate the mass from 0-1000km&#x2F;h, it will take 4 Joules to accelerate the same mass from 0-2000km&#x2F;h.<p>Elon is calling that <i>four times as much as</i> because he&#x27;s considering the total energy required to accelerate from 0 in both numbers.  I think you&#x27;re just accounting for it differently by saying it takes 3 times as much as the original energy input to go from 1000km&#x2F;h to 2000km&#x2F;h.<p>I&#x27;m a complete physics novice, I&#x27;m open to being schooled on this if I&#x27;m completely missing both yours and Elon&#x27;s concepts here.