Simultaneity question: light in a moving spaceship

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Homework Help Overview

The problem involves a spaceship moving at a velocity of 0.2c with light sources positioned at both the back and front. The questions focus on the time it takes for light emitted from the back to reach the front and vice versa, considering the spaceship's motion.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the concept that light travels at speed c in all reference frames, leading to an initial calculation of time based on distance and speed. However, they express uncertainty about the correctness of their reasoning.
  • Some participants suggest considering the frame of reference where the spaceship is moving, indicating a potential oversight in the original poster's assumptions.
  • There is a clarification regarding the measurement frame, with the original poster noting that the time should be measured from the spaceship's frame.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem. Some guidance has been provided regarding the frame of reference, but there is no explicit consensus on the final answers yet.

Contextual Notes

The original poster mentions a concern about their initial reasoning and the implications of measuring time from the spaceship's frame, indicating a need for further clarification on the assumptions involved.

senorhosh
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Homework Statement


Spaceship with proper length 100m is moving at 0.2c in +x direction. In the back and front of the spaceship is a light source.
a. When the light in the back is turned on, how long will it take for the light to reach the front of the spaceship?
b. How about the light in the front? (to reach the back)

Homework Equations





The Attempt at a Solution


a. I'm guessing because light always moves at c in all reference frames, t = d/c or 100/c? There would be no time dilation or length dilation because light is moving the same frame as the space ship
b. Same answer as a. for the same reasons.

For some reason, I don't think this is correct. I'm not sure why... it just seems off..
Any help? thanks.
 
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I suspect they want the time it takes for the light to travel according to the frame that views the rocket as moving at 0.2c.
 
Doc Al said:
I suspect they want the time it takes for the light to travel according to the frame that views the rocket as moving at 0.2c.

Whoops I forgot to add this in.
"Measured by the frame of the spaceship". So no..
sorry about that. Anyway would my answer be correct then?
 
senorhosh said:
Whoops I forgot to add this in.
"Measured by the frame of the spaceship". So no..
sorry about that. Anyway would my answer be correct then?
Yes, in that case your answers are correct: the time of travel is simply 100m/c in each direction. (From the frame of the rocket, the rocket is at rest.)
 

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