# Homework Help: A question on relativity

1. Sep 19, 2004

### stunner5000pt

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

2. Sep 19, 2004

### jcsd

Look at c) again.

3. Sep 19, 2004

### stunner5000pt

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?

4. Sep 19, 2004

### jcsd

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.

5. Sep 19, 2004

### HallsofIvy

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.

6. Sep 19, 2004

### stunner5000pt

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