Doppler Effect Source Moving Away

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SUMMARY

The discussion centers on calculating the speed at which Superman must fly away for his blue light (480nm) to appear orange (600nm) using the Doppler Effect. The initial attempt used the formula f' = f / (1 + v_s / v) but yielded an incorrect speed of 75×10^8 m/s, while the correct range is between 57.0×10^6 m/s and 67×10^6 m/s. A participant suggested using the relativistic Doppler effect equation λ = λ₀√((1 - β) / (1 + β)), which is necessary for accurate results in this scenario due to the high speeds involved.

PREREQUISITES
  • Understanding of the Doppler Effect
  • Familiarity with wave properties, specifically wavelength and frequency
  • Knowledge of special relativity concepts, particularly time dilation
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Study the relativistic Doppler effect and its applications
  • Learn about the relationship between wavelength, frequency, and speed of light
  • Explore the implications of special relativity on classical physics equations
  • Practice problems involving the Doppler Effect with varying velocities
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Physics students, educators, and anyone interested in understanding the Doppler Effect and its applications in relativistic contexts.

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Homework Statement


Superman has a blue light of wavelength 480nm. How fast must he fly away from you so that his light appears orange, with a wavelength of 600nm?

Homework Equations


f'=\frac{f}{\left(1+\frac{v_s}{v}\right)}
and
f=\frac{c}{\lambda}

The Attempt at a Solution


I used the equation f'=\frac{f}{\left(1+\frac{v_s}{v}\right)} and solved for v_s and got my answer to be 75\times 10^8 m/s but the answer key said 57.0\times10^6 - 67\times10^6m/s. What did I do wrong?
 
Last edited:
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Someone told me that the equation \lambda =\lambda_{0}\sqrt{{1-\beta}\over{1+\beta}} give the correct answer (like the other thread). Why didn't the usual doppler effect equation work here? I'm confused.
 

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