Speed relativity, Einsteins theorie

[slrn]

Homework Statement

astronaut has 8 years to get to a solar system that earthlings see is 80c years from earth. How fast does the astronaut have to go to get there in 8 years.

Homework Equations

L=L0(sqrt(1-(v/c)^2)
L0/T=L/T0

The Attempt at a Solution

L0 = 80 cyears
T0 =8 years

 

[Doc Al]

Hint: Express the speed in terms of distance and time.