Physics wave question

[roxxyroxx]

Homework Statement

a spectral line coming from a star in a binary system has a wavelength of 515.2 nm. in the lab the same spectral line would have a wavelength of 518.6 nm. what is the speed of the star in relation to earth?

Homework Equations

??

The Attempt at a Solution

??

 

[crazy_photon]

look up doppler effect, i'm not going to propose solution, because once you learn it for yourself -- I'm sure you'll figure it out in an instant (at least in a classical sense, not accounting the general relativity corrections -- there's not enough info in the problem to use that anyway).

 

[Phrak]

Or you could try relativistic doppler effect.

 

[Ilivian]

Use the Dopple formula:

f'=f.V/(V+Vs)

V=c=3.10^8 m/s :speed of the radio wave.
Vs: velocity of the star (source).

U should find Vs, if it's positive then the star is moving away from the earth, otherwise it's moving closer.