Two people are on a train that is moving at 10 m/s north. They are walking 1 m/s south relative to the train. Relative to the ground, their motion is 9 m/s north.

Question

Why are we able to use these motions to describe the motion relative to the ground?

(1 point)
Responses

The people are moving much slower than the speed of light so the ground acts as a frame of reference.
The people are moving much slower than the speed of light so the ground acts as a frame of reference.

The motion of everything in the Universe besides light can be described in this way.
The motion of everything in the Universe besides light can be described in this way.

If one object is moving much slower than the speed of light, its speed can be added to that of another object.
If one object is moving much slower than the speed of light, its speed can be added to that of another object.

As long as the frame of reference is stationary, all motion can be described in this way.

Answer 1

The correct response is:

If one object is moving much slower than the speed of light, its speed can be added to that of another object.

This statement reflects the classical mechanics principle of relative motion, which allows us to simply add or subtract velocities when dealing with objects moving at speeds much slower than the speed of light. In this scenario, the velocities of the people relative to the train and the train relative to the ground can be combined to find their velocity relative to the ground.