How can the Doppler effect of light determine an astronaut's speed?

[jessicah]

Homework Statement

An astronaut is said to have tried to get out of a traffic violation for running a red light (lambda= 670nm) by telling the judge that the light appeared green (lambda= 540nm) to her as she passed by in her high powered transport. If this is true, how fast was the astronaut going?

Homework Equations

Lambda= c(T_period)

The Attempt at a Solution

5.40X10^-7m= 3.00x10⁸( T)
T= 1.8x10^-15sec

Im not sure if this is the correct approach but once you get the time how do you get the speed?

Homework Equations

The Attempt at a Solution

 

[gabbagabbahey]

Hi Jessicah, welcome to PF!

5.40X10^-7m= 3.00x10⁸( T)
T= 1.8x10^-15sec

Im not sure if this is the correct approach but once you get the time how do you get the speed?

Well, since this is a problem on the relativistic Doppler effect, you might try reading about the effect in your textbook and finding the equation for Doppler shift...