# Homework Help: Physics Relativity Question?

1. Feb 6, 2012

### justinh8

Physics Relativity Question????

1. The problem statement, all variables and given/known data
I need some help with this,
A train moves at a constant velocity of 21 m/s. The end of the train passes a sign at 12 noon and 4 seconds later a conductor starts collecting tickets starting with a passenger sitting 25m from the rear of the train. Another passenger located 55m from the rear of the train reads the newspaper at noon and finishes 42 seconds later. What is the Spatial Separation of these events in the frame of reference of the train and the earth???

2. Relevant equations
delta x = delta x' + v x delta t

3. The attempt at a solution
What i did was i found the difference of the two events and the difference in the x was 30m. the difference in the time was 38 seconds and once i plugged it in the equation i got 828m. Idk if this is right or wrong nor do i know if this is in the frame of reference of the earth or the train

2. Feb 6, 2012

### justinh8

Re: Physics Relativity Question????

anyone wanna help?

3. Feb 6, 2012

### SammyS

Staff Emeritus
Re: Physics Relativity Question????

Physics Forum Rules include the following regarding the practice of "bumping".
Do not "bump" one of your threads to the top of a forum's thread list by posting a basically empty message to it, until at least 24 hours have passed since the latest post in the thread; and then do it only once per thread.​
You managed to wait all of 81 minutes.

4. Feb 7, 2012

### SammyS

Staff Emeritus
Re: Physics Relativity Question????

My first question is: What events is it asking about? There are at least three.

At 12:00:04, the conductor collects a ticket from passenger A, who is sitting 25m from the rear of the train.

At 12:00:00 a passenger B, who is 55m from the rear of the train, begins reading the newspaper.

At 12:00:42 the passenger B finishes reading the newspaper.​
Other possible events include:
Passenger A passing by the sign.

Passenger B passing by the sign.

The rear of the train passes by the sign.

We could also count the entire 42 seconds worth of passenger B reading the paper. If so, that event may span more than a single point in space, depending upon the frame of reference.

The spacial separation of most of these events, in the reference frame of the train is pretty obvious.

By what distance are they separated in the frame of reference of the earth ?

5. Feb 7, 2012

### justinh8

Re: Physics Relativity Question????

Ya, i think were not taking about the event of the women that was 25 m from the rear so i think you can just erase that part (my teacher cleared it up) so in reference to the earth, would it just be delta x = 0 + 21(42)? that would be my guess but im not sure. and if it was reference to the bus, it would be just zero right?

6. Feb 7, 2012

### SammyS

Staff Emeritus
Re: Physics Relativity Question????

What bus ?