Final answer:
When dogs make inelastic collisions in the back of a coasting pickup truck, it does not change the truck's center of mass, but it may cause minor internal motions. In running down stairs and stopping, a person's kinetic energy dissipates, and their gravitational potential energy decreases as it converts to kinetic energy.
Step-by-step explanation:
The question pertains to the effects of motion within a system, specifically focusing on a pickup truck and its load. The truck is coasting with negligible friction, which in physics terms means that external forces from friction are not significantly impacting the truck's motion. As for the dogs in the back of the truck, while they are moving and making inelastic collisions with each other and the walls of the truck, they do not alter the center of mass of the system (the truck and its entire load). The center of mass represents the average position of all the mass in the system, and it will not change unless an external force acts on the system. However, the dogs' actions could create internal forces that possibly cause the truck to rock or jitter, though they would not affect the truck's overall motion toward the stoplight.
Similarly, when a person runs down the stairs and comes to a stop, their kinetic energy is dissipated through friction and air resistance, often perceived as heat and sound. Additionally, as they descend the stairs, their gravitational potential energy decreases because their height relative to the base decreases. This gravitational potential energy is converted into kinetic energy until they stop.