# Velocity with relativity

Find the speed of a particle that takes 2.0 y longer than light to travel a distance of 6.7 ly. Answer is wanted in terms of 'c'.

delta(t)= delta(t0)/(sqrt(1-(v/c)^2)).

8.7= 1/(sqrt(1-(v/c)^2))-->
1/8.7=sqrt(1-(v/c)^2-->[/b]
(1/8.7)^2=1-(v/c)^2-->[/b]
(v/c)^2=1-(1/8.7)^2-->[/b]
v/c=sqrt(1-(1/8.7)^2)-->[/b]
v/c=0.993372-->
v=0.993372c....which is incorrect, any assistance would be greatly appreciated[/b]
note: I also tried delta(t) to be 4.7...also incorrect

## The Attempt at a Solution

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dx
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What is the speed of light in units of light-years per year? It's just one! Light travels one light-year per year.

The particle travels 6.7 light-years in (6.7 + 2) years, so it's speed in units of light-years per year is ... ?

What is the speed of light in units of light-years per year? It's just one! Light travels one light-year per year.

The particle travels 6.7 light-years in (6.7 + 2) years, so it's speed in units of light-years per year is ... ?
Thank you so much!! That makes perfect sense. I hate when I over-complicate problems like these. Much appreciated!