What might happen to the human heart during a trip to mars?
a. stop working completely
b. become too weak to pump blood
c. expand and become too large to work properly

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