Systems with Varying Mass: A Rocket
In the systems we have dealt with so far, we have assumed that the total mass of the system remains constant. Sometimes. as in a rocket it does not. Most of the mass of a rocket on its launching pad is fuel. all of which will eventually be burned and ejected from the nozzle of the rocket engine.
We handle the variation of the mass of the rocket as the rocket accelerates by applying Newton’s second law, not to the rocket alone but to the rocket and its ejected combustion products taken together.The mass of this system does change as the rocket accelerates.