# 2D Relativity Problem solving

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1. Jul 3, 2015

### pablodel

• Missing homework template due to originally being posted in other forum.
Hello my name is Pablo, i'm new in the forum and couldn't find any similar post so i decided to ask. I have the following situation:
In reference frame S (asumed stationary) there is a stick (length Lo in frame S) which falls from Yo at a vertical speed of 0.6c relative to S. In S the stick is horizontally positioned.
There's also another reference frame, S' which moves at 0.8c (positive x) relative to S (note that x and x' are aligned and y is parallel to y'). So i've got an object moving only vertically in a stationary reference fram and another reference frame which moves horizontally relative to the other frame.
I need to calculate which end of the stick gets to y'=0 first and also the tangent of the angle it forms when it first touches the ground. Finally i have to calculate the kinietic energy in terms of the stationary mass.

I used the Laurentz time transformation to get the contact timie for each of the ends of the stick in S' assuming the time in S is t=Yo/0.6c.
For the next step i did the following: the Δx'=Lo/γ and (i do not trust myself in this one) ΔY'=u'*Δt' where u' is the Lorentz transformation of the vertical speed relative to S and Δt' is the difference between the times i calculated previously. Is this correct? if it is not ok how can i solve this?
Thanks a lot

2. Jul 4, 2015

### Staff: Mentor

How about you start with defining two events: The left side of the stick reaches ground level and the right side of the stick reaches ground level. What are the spacetime coordinates of those events in S? Then use the Lorentz transformation to calculate their spacetime coordinates in S'.