Final answer:
Option 1: Momentum changes for a cannonball when fired, but within the system including the cannon, momentum is conserved.
Step-by-step explanation:
When a cannonball is fired from a cannon, its momentum does indeed change because it goes from a state of rest to a state of motion with a certain velocity. However, if we look at the cannonball and the cannon together as a system, momentum is conserved within that system. According to the law of conservation of momentum, the momentum before firing (when both cannon and cannonball are at rest) is equal to the momentum after firing (cannon moves backward, and cannonball moves forward). While kinetic energy may not be conserved due to transformation into other forms of energy, such as heat and sound, the momentum is conserved provided no external forces are acting on the system. This conservation applies to closed systems not subjected to external forces, which is a fundamental principle in physics.
For instance, when we observe a collision in a sport like tennis, the momentum of the ball changes when hit by a racket. But if we consider the ball, the racket, and the player as a single system, the overall momentum of this system is conserved. This is because the momentum lost by the ball is gained by the racket (and possibly by the player holding the racket). The law of conservation of momentum is a fundamental principle in physics that applies to all interactions where no external forces are involved.