Question

a train moving near the speed of light enters a tunnel. according to a person standing in the middle of the tunnel, the back end of the train enters the tunnel just as the front end is emerging. what happens according to someone sitting in the middle of the train? a. the back end enters the tunnel at the same time as the front end emerges. b. the back end enters the tunnel before the front end emerges. c. the front end leaves the tunnel before the back end enters. d. the front end leaves the tunnel at the same time the back end passes the person standing in the middle of the tunnel. e. the front and back ends of the train enter the tunnel at the same time.

Explanation:

Step1: Understand relativity of simultaneity

In special - relativity, events that are simultaneous in one frame of reference may not be simultaneous in another moving frame.

Step2: Analyze the situation

A person in the middle of the tunnel is in a non - moving frame relative to the tunnel. When light enters the tunnel, due to the finite speed of light and the motion of the train, from the perspective of the person in the middle of the tunnel, the front end of the train enters the tunnel before the back end emerges. This is because the light from the front end of the train has to travel a shorter distance to reach the observer in the middle of the tunnel compared to the light from the back end of the train.

Answer:

B. The back end enters the tunnel before the front end emerges.