Question

An observer sees an airplane flying at a fast, constant speed along a straight path. However, a passenger inside the airplane feels that they are not moving at all.

What explains the difference between what the observer is seeing and what the passenger is feeling?

A.
The observer is moving at the same velocity as the plane, so the net force on the observer is zero.
B.
The acceleration of the observer is in the opposite direction of the motion of the airplane, so the net force on the observer is decreasing.
C.
The acceleration of the passenger is in the same direction as the motion of the airplane, so the net force on the passenger is increasing.
D.
The passenger is moving at the same speed as the plane, so the net force on the passenger is zero.

Answer 1

D.

The passenger and the plane share the same constant velocity, so the passenger has no acceleration and thus no net force acting on them. Sensation of motion comes from acceleration (changes in speed or direction), not from uniform motion; the external observer simply measures the plane's motion relative to the ground.