From a stationary position,I observe a moving boxcar,which has a mirror along the front wall,but it is open at the back of the boxcar.I send a flash of light from my flashlight and time the flash of light as it goes to the front of the boxcar and returns to the back of the boxcar.A passenger in the boxcar also times the round trip of the flash of light.Previously I had measured the time required for the round trip of a flash of light when the boxcar was stationary,and I call this the stationary time.Which two times are the same?
A)the time recorded on my watch and the previous stationary time
B)the time recorded on the passenger's watch and the previous stationary time
C)the time recorded on my watch and the time recorded on the passenger's watch
D)None of the times are the same.

Question

Quizplus · Accepted Answer

The time recorded on the passenger's watch and the previous stationary time are the same because, according to the principle of relativity, the laws of physics, including the speed of light, are the same in all inertial frames. The passenger in the boxcar is in an inertial frame where the boxcar is stationary, so they measure the same time as when the boxcar was previously stationary.

From a Stationary Position,I Observe a Moving Boxcar,which Has a Mirror