Final answer:
An object with mass and motion is associated with momentum, a measure of its motion, which is conserved in a closed system. Inertia is the property that measures an object's resistance to changes in motion, related to its mass.
Step-by-step explanation:
An object that has mass and is moving is associated with momentum. Momentum is a vector quantity that is the product of an object's mass (m) and its velocity (v). Essentially, it's a measure of the amount of motion an object has, and it's directly proportional to both mass and velocity. For example, if two objects have the same velocity, the one with greater mass will have more momentum.
Momentum is conserved in a closed system where no external forces are acting. This means that in a collision, such as in the example where mass A collides with mass B, the total momentum before the collision is equal to the total momentum after the collision, complying with the law of conservation of momentum.
Inertia is another important concept related to mass, representing the resistance of any physical object to any change in its velocity. This includes changes to the object's speed, or direction of motion. A large, slow-moving object can have significant momentum due to its mass, making it more difficult to stop or change its direction, illustrating the concept of inertia.