# Homework Help: Relativity - world lines

1. Jan 11, 2014

### Andy93

1. The problem statement, all variables and given/known data
A light source at the origin of the O frame emits short pulses of light in interval of $\tau$ as measured in O. An observer located at the origin of the O' frame which moves at velocity v with respect to O along the x-axis, receives these light pulses.
Use a world line diagram to show the receipt of two consecutive pulses as measured in O if the first is emitted when the frame origins coincide. Show that measured in O the pulses are received at the origin of O' with the temporal separation of (c$\tau$)/(c-v) and spatial separation of (c$\tau$v)/(c-v).

2. Relevant equations

3. The attempt at a solution
The pulses of light travel at velocity c
The receiver travels at velocity v
I have drawn the world line (t-x plot) and I'm pretty sure it's Δt and Δx i need to calculate but i'm not sure how to go about it.
http://img24.imageshack.us/img24/4083/z559.png [Broken]

Last edited by a moderator: May 6, 2017
2. Jan 11, 2014

### vela

Staff Emeritus
Your diagram looks good. Now you're trying to find where the two lines intersect. This is just like what you did in algebra class, except this time the variables are x and t instead of x and y.

Start by figuring out the equations for the two lines.

3. Jan 11, 2014

### Andy93

I didn't realise it would be so simple, thanks a lot for the help. It worked out perfectly.