(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A spaceship moves radially away from the earth with an acceleration of 20m/c^{2}. How long does it take the sodium street lamps ([tex]\lambda[/tex]=589 nm) on earth to be invisible (with a powerful telescope) to the human eye of the astronauts? The visible spectrum is 400-700nm.

2. Relevant equations

f_{obs}= ((1+(v/c))^{1/2}/(1-(v/c))^{1/2}) f_{source}

3. The attempt at a solution

I can use the doppler shift equation, to solve for velocity, but what should I use for f_{obs}? Should I use 400nm or 700nm. I'm thinking 400 nm because of length contraction...

After I find a velocity, I can use the acceleration given and solve for time.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Spaceship moving away from light source

**Physics Forums | Science Articles, Homework Help, Discussion**