(Seeing is not the same as observing!). Imagine that a bullet train running at a
ID: 2075460 • Letter: #
Question
(Seeing is not the same as observing!). Imagine that a bullet train running at a very high speed passes two track-side signs (A and B), as shown in the aerial view in the figure. The blue squares represent the train wagons and the red square represents the engine. Let event A be the passing of the front end of the train by sign A and event B be the passing of the rear end of the train by sign B. An observer is located at the cross marked by an O in the diagram. The distances are d_1 = 80 ns, d_2 = 45 ns, d_3 = 60 ns. This observer sees (i.e. receives light with her eyes) event A to occur at time t = 25 ns. When does she observe these events to occur? That is. what would a clock present at sign A read at event A, and what would a clock present at sign B read at event B if these clocks were correctly synchronized with the clock at O? In what way is the diagram above misleading about the implied time relationship between the events A and B?Explanation / Answer
d1 = 80ns-c, d2 = 45ns-c ; d3 = 60ns-c
BO = sqrt(802 +602) = 100ns-c
AO = sqrt(452 +602) = 75ns-c
light from A to O takes 75ns and that from B to O takes 100 ns to travel.
a) observer at O sees event A occur at 25s ,
The event has occured 75ns before she recoves the light, clock at A would read 25 +75 = 100 ns when Observer sees event A.
Clock at B would also read 100 ns at this point of time as events A and B are simultaneous and all the clocks are synchronised.
b) the diagram implies the events A and B are simultaneous.
b)
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