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

How fast would a star have to travel to make violet light (λ = 400 nm) appear to be blue (λ = 450 nm)? Assume the star is moving along the line that connects the star to the Earth.

2. Relevant equations

λr = λc / (c-Vr)

f= fo (c +- Vr / c +- Vs)

3. The attempt at a solution

Well, to be honest I am completely confused with this problem. It is the last problem in a homework set, so it is most likely the most difficult.

First attempt:

400-450 = -5e-8.

Now solve for v:

Δf = fs*((1+v)/c)

v = Δf*c/fs-1 = -5e-8*3e8/(4e-7) - 1 = -3.75E7 m/s, so the star would have to be moving away from you at 37,500,000 m/s.

Second attempt:

Vr = 450 * 3e8 / 400 * 3e8 = 1.125.

Neither are correct. Any assistance or guidance is truly appreciated. Thank you.

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Use doppler shift to find star velocity

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