A rocket has mass $M$ when it is empty. It also carries an extra mass $M$ of fuel. The rocket and the fuel are moving at speed $v$. When the rocket engine is ignited, all of the fuel is ejected and the rocket’s speed rises to $2v$. What happens to the kinetic energy of the rocket?
- AIt doubles.
- BIt halves.
- CIt increases by a factor of four.
- DIt stays the same.