# Homework Help: Basic S.T.R. problem. K vs K' systems.

1. Sep 7, 2010

### amcelroy13

1. The problem statement, all variables and given/known data

An event occurs in system K' at x' = 2 m, y' = 3.5 m, z' = 3.5 m, and t' = 0. System K' and K have their axes coincident at t = t' = 0, and system K' travels along the x axis of system K with a speed 0.92c. What are the coordinates of the event in system K?

2. Relevant equations

x' = $$\gamma$$(x-vt)
t' = $$\gamma$$(t-(v/c^2)x)

3. The attempt at a solution

I know that, as the system is not moving in either the y or z directions that y and z are the same, so y=3.5m and z=3.5m. I feel as though t should = 0, because in the problem statement it clearly says that "their axes coincident at t=t'=0 so if t'=0 then t should =0, but I've been told that's not right... I'm completely at a loss for x.

2. Sep 8, 2010

### vela

Staff Emeritus
What that means is (t,x)=(0,0) and (t',x')=(0,0) are the same point. It doesn't say anything about points other than the origin. It's like rotations of the xy-plane. The origin for both the unrotated and rotate axes coincide, but other points on the x-axis don't lie on the x' axis. Similarly, just because a point lies on the t'=0 line, it's not going to be on the t=0 line.