можно я сддесь буду задавать вопросы? итак

1. a gun fires a bullet. before the event both the gun and the bullet are at rest so their total momentum is zero. after the bullet is fired it has momentum. and the gun has momentum opposite that of the bullet.
does it mean there we have two sets of momenta? 1. objects at rest 2. objects in motion? if so what needs to be done to preserve them? thanks.

2. consider a wreck in which a car runs into a back of a truck. before the collision the car has momentum forward. suppose the car and the truck stick together after the crash. the law of conservation tells us that the momentum of the wreckage will be same as the momentum of the car before collision. how so? didnt the truck stop the car in its tracks and bring its speed to zero? how is zero equal to the car`s initial speed?