# Basic Special Relativity

PsychonautQQ

## Homework Statement

A star is 27c*y away from the rest reference of earth. A rocket reaches star A from earth and according to clocks on it 12 hours have passed. How fast is the rocket traveling in earth's reference frame?

tpγ=t
Lp/γ=L

## The Attempt at a Solution

The problem is under the category of length contraction and time dilation so I assume these are the two equations I must use. However when trying to do the problem I only was given t and Lp, and yet there are three variables (tp, L, and v). Help ;-(

Enigman
Can you calculate what time has passed wrt IRearth?
(I am assuming Earth is assumed to be an IR and the ship doesn't accelerate.)

PsychonautQQ
yes, no acceleration.
I don't think I can calculate the time wrt IRearth..? I would need to know the velocity to do that so I knew the gamma factor correct?

Enigman
vearth=dearth/tearth
tearth=dearth/vearth
plug and chug.

PsychonautQQ
I don't know t_earth though? I only know it took 12 years from the spaceships frame..? oh... is Vearth 27c*y / 12 years...? i'm a noob X_X

PsychonautQQ
but that's not REALLY the speed earth see's it moving is it? Because earth couldn't see the rocket traveling faster than C could it?

Enigman
vearth=dearth/tearth
tearth=dearth/vearth
plug and chug.

tearthγ=t
or, tearth=t/γ
equate the tearth