What is an astronomical unit? why is this unit used to measure distances in the solar system?

Are the earth's ocean floor and continents the same age geologically? why or why not?

What does natural resource management aim at ?

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point