Speed of two spaceships relative to each other observed by an earth observer

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Discussion Overview

The discussion revolves around the calculation of the relative speed of two spaceships approaching each other as observed by an Earth observer. It explores concepts related to relativistic speed addition and the implications of maximum speed limits in physics.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant presents a scenario where two spaceships are each traveling at 0.8c towards Earth and questions how to calculate their relative speed as they approach each other.
  • Another participant mentions the term "closing speed" and suggests that while the calculated value may be straightforward, it does not reflect the actual speeds of the spaceships relative to one another.
  • There is a suggestion to refer to "velocity addition" for a deeper understanding of the relative speeds involved.
  • One participant clarifies that the question is based on past exam questions rather than being a homework assignment.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method of calculating the relative speed, with differing views on the implications of the calculated values and the concept of closing speed.

Contextual Notes

The discussion does not resolve the mathematical steps involved in relativistic velocity addition, and there are assumptions regarding the definitions of speed and closing speed that remain unaddressed.

salmise
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Edit. I think the topic is misinformative and I don't know how to change it.

Hey

I have to translate this into english so bear with me.

Two spaceships are approaching Earth from two directions along the x-axis. Earth observer(EO) calculates their speeds to be 0,8c each. Calculate at what speed EO observes them to be approaching each other.

Is c the maximum speed in situations like this or can you just add the speed together -> 1,6c?
 
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salmise said:
Two spaceships are approaching Earth from two directions along the x-axis. Earth observer(EO) calculates their speeds to be 0,8c each. Calculate at what speed EO observes them to be approaching each other.

Is c the maximum speed in situations like this or can you just add the speed together -> 1,6c?
Is this a homework question?
 
Nope, I am just going through the questions from past exams.
 
The term that is usually applied in situations like this is "closing speed" and it is equal to the value you got but it is just a calculation and not related to the actual speed that anything is traveling at. Look up "velocity addition in wikipedia if you want to see what each spaceship is actually traveling relative to the other one.
 

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