Calculating Train Speeds Using Classical Relativity

  • Thread starter Thread starter stunner5000pt
  • Start date Start date
  • Tags Tags
    Relativity
Click For Summary

Homework Help Overview

The discussion revolves around calculating the relative speeds of two trains using classical relativity. The original poster presents a scenario involving two trains moving in opposite directions and a ticket collector moving within one of the trains. The focus is on determining the speeds as perceived by different observers, specifically using Galilean transformation equations.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the calculations of relative speeds from various perspectives, including an observer at the station, a passenger on the westbound train, and the ticket collector. There are questions about the validity of the calculations, particularly regarding the speed perceived by the ticket collector and the assumptions made in the original problem.

Discussion Status

Some participants are questioning the correctness of the original calculations, particularly in relation to the ticket collector's perspective. There is an ongoing examination of the assumptions and definitions used in the problem, with no clear consensus reached yet.

Contextual Notes

Participants note the importance of distinguishing between classical and special relativity in their calculations. There is also mention of potential misunderstandings regarding the phrasing of the question and what is being asked about the relative speeds.

stunner5000pt
Messages
1,447
Reaction score
5
The classical kind, of course

If two trains leave a station o nteh same track. An observer missed both these trains and is standing clsoe to the track sees the westboun train recede at 0.6c and sees the eastbound train recede at 0.8c. There is a ticket collector on the westbound train going from the back of the train to the front at 0.4c, with respect to a passenger on the westbound train.


If the GALILEAN transformation equations were true then what would the speed of the eastbound train with respect to the westbound train (call it Ur) according to:

A) Observer on the station - i would say 1.4c because that what he sees, right?

b) Passenger seated on the westbound train - 1.4c becasue if he looked behind out hte window he would see the eastbound train go 0.8c + 0.6c away from him

c) Ticket collector on the westbound train (still walking from back to the front) - 1.8c (her speed 0.4c + speed of train 0.6c + speed of east train 0.8c)

Similarly what is the speed of the ticket collector:

d) according to the observer on the station - 1c - speed of the train + TC speed

e) according to passenger seated o tneh east train - 1.8 c


f) relative to a passenger seated on the east train according to to the observer on the station - 1.8c

remember this is using classical relativity, not special relativity, please tell me if i made any mistakes
 
Physics news on Phys.org
Look at c) again.
 
jcsd said:
Look at c) again.
what's wrong with it??

the ticket collector is moving the back of the west train to the front at 0.4c while the train is moving at 0.6c in the same direction if she looekd back then she would see the east train move at train speed + her speed +east train speed, right?

what am i missing here?
 
Unless you missed out something in the original question, the question doesn't seem to be asking what speed does the ticket collecter see the train move at.
 
What jcsd is saying is that the question specifically asks "what is the speed of the east bound train with respect to the west bound train [\b] accoording to ...

In c, your answer is the speed of the east bound train with respect to the conductor. Using Galilean physics, everyone should say that the speed of the east bound train relative to the west is 0.8c+ 0.6c= 1.4 c.
 
HallsofIvy said:
What jcsd is saying is that the question specifically asks "what is the speed of the east bound train with respect to the west bound train [\b] accoording to ...

In c, your answer is the speed of the east bound train with respect to the conductor. Using Galilean physics, everyone should say that the speed of the east bound train relative to the west is 0.8c+ 0.6c= 1.4 c.

so am i right or what?? you just explained my own understanding, and thus if that were true then the collector who is movin at 0.4c westbound would see the speed of her, the train and the east train as the speed of the eastbound train's recedance
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
Replies
2
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 26 ·
Replies
26
Views
6K
  • · Replies 52 ·
2
Replies
52
Views
9K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 14 ·
Replies
14
Views
4K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K