Why a reference point must be stationary?

To practice problem-solving strategy 10.1 for energy conservation problems. a sled is being held at rest on a slope that makes an angle θ with the horizontal. after the sled is released, it slides a distance d1 down the slope and then covers the distance d2 along the horizontal terrain before stopping. find the coefficient of kinetic friction μk between the sled and the ground, assuming that it is constant throughout the trip.

Which if these is an etiquette rule? (american football) question 10 options: a. debating with the ref over a call b. not communicating with your team c. post-game handshake d. taunting

Organ systems work to maintain homeostasis by creating energy to allow systems to function, releasing hormones to create or end body reactions, and eliminating waste to prevent illness. t or f