Speed of Ships -- Special Relativity

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Homework Help Overview

The problem involves the relative speeds of a spaceship and galaxies, specifically applying concepts from special relativity to determine the speed of the spaceship as observed from another galaxy. The context centers around velocity addition in relativistic physics.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the initial assumption about the spaceship's speed and question the application of velocity addition in special relativity. There is a focus on understanding how the relative motion of the galaxies affects the observed speed of the spaceship.

Discussion Status

Some participants have offered insights into the principles of velocity addition, while others have expressed uncertainty about the direction of the spaceship's motion relative to galaxy A. Multiple interpretations of the problem are being explored, and there is an ongoing examination of the assumptions made regarding the directions of motion.

Contextual Notes

There is a mention of ensuring that the sum of the speeds does not exceed the speed of light, indicating a constraint related to relativistic physics. The discussion reflects the complexity of interpreting relative velocities in a relativistic framework.

Barry Melby
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Homework Statement


Galaxy A moves away from galaxy B at 0.650 c0 relative to B. A spaceship leaves a planet in galaxy A traveling at 0.550 c0 relative to galaxy A. If the direction in which the ship travels is the same as the direction in which A is moving away from B, what do observers in B measure for the ship's speed?

Homework Equations



The Attempt at a Solution


I thought that the speed would be .550c , but this appears to be incorrect. Any thoughts?
 
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That would be slower than galaxy A is moving.

What do you know about velocity addition?
 
From B's point of view, A is moving away at 0.65c. Since the spaceship is moving away from A in the direction of B at 0.55c, B will see the ship move away - but not as fast as 0.65c.
 
.Scott said:
From B's point of view, A is moving away at 0.65c. Since the spaceship is moving away from A in the direction of B at 0.55c, B will see the ship move away - but not as fast as 0.65c.
I don't think that is right. I believe the ship is moving in the opposite direction from A.
 
PeroK said:
I don't think that is right. I believe the ship is moving in the opposite direction from A.
If the direction in which the ship travels is the same as the direction in which A is moving away from B
You're right. So it's simple relativistic addition.
Just make sure 0.65+0.55<1
 

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