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

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

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.

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, where velocities are additive when dealing with objects moving at speeds much less than the speed of light. In this scenario, the train moves north at 10 m/s, and the people walking south at 1 m/s relative to the train can have their speeds added to find their overall motion relative to the ground.