Suppose the observer on the train in the figure aims her flashlight at the far wall of the boxcar and turns it on and off, sending a pulse of light toward the far wall. Both and measure the time interval between when the pulse leaves the flashlight and when it hits the far wall. Which observer measures the proper time interval between these two events? (a) (b) (c) both observers (d) neither observer.
(a) A mirror is fixed to a moving vehicle, and a light pulse is sent out by an observer at rest in the vehicle.
(b) Relative to a stationary observer standing alongside the vehicle, the mirror and move with a speed v, and the light pulse follows a diagonal path.
(c) The right triangle for calculating the relationship between and .
