I answered this here: https://physics.stackexchange.com/questions/287101/where-does-the-extra-kinetic-energy-of-the-rocket-come-from/287102#287102 https://physi

I answered this here: https://physics.stackexchange.com/questions/287101/where-does-the-extra-kinetic-energy-of-the-rocket-come-from/287102#287102 https://physics.stackexchange.com/questions/287101/where-doe... The basic answer is that the extra energy that goes to the rocket comes from harvesting the kinetic energy that the fuel itself had by virtue of being in the moving rocket.