When two different observers watch a moving object,

a. they always see different motion
b. both of them always see the same motion
c. both of them see the same motion as long as both of them are moving
d. they will see the same motionvif they are in the same reference frame

Arunner is training for an upcoming marathon by running around a 100-m-diameter circular track at constant speed. let a coordinate system have its origin at the center of the circle with the x-axis pointing east and the y-axis north. the runner starts at (x, y) = (50 m, 0 m) and runs 2.5 times around the track in a clockwise direction.