Question

A stationary observer at a railway station sees a passenger in a railway coach that is in motion at constant speed in a straight and horizontal track. Which of the following best descibes the frames of reference from which both the observer and the passenger descibe each other's motion?

Answer 1

Both the observer and the passenger move with constant velocity relative each other. Thus, the frames of reference from which both the observer and the passenger describe each other's motion are inertial frames.

Answer: inertial.