Question

The people on the roller coaster are in motion relative to the people waiting in line.

Answer 1

This sentence is true because as the motion is relative, that means that it depends of the point of view. The person that is in the roller coaster is static in his or her position and what is movin is the roller coaster, and the person that is waiting in the line is static. So in this case as it depends of the point of view that menas that this sentence is true.