The Street Lamp Problem
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- 5 street lamps A, B, C, D, and
E are located on a straight
line along the x axis equal distance apart as shown in the figure.
They turn on at times tA, tB,
tC, tD, and tE,
respectively, in the frame at rest relative to the ground.
This is indicated in the space-time diagram above the figure.
What is the order in which the lamps turn on in this frame?
- What is the order in which the light of the lamps reach the
observer at x=0?
- A car is moving at constant velocity relative to the ground.
At t'=t=0, it is at x'=x=0.
The space and time axes in the moving frame of the car are tilted
with respect to those of the rest frame as shown in the space-time
diagram. What is the order in which the lamps turn on
in this frame?
- What is the order in which the light from the lamps reach the
observer riding the car?
- Where is the car when the light from street lamp D reaches it?