Doppler Effect Source Moving Away

  • Thread starter JSGandora
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JSGandora
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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


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


The Attempt at a Solution


I used the equation [itex]f'=\frac{f}{\left(1+\frac{v_s}{v}\right)}[/itex] and solved for [itex]v_s[/itex] and got my answer to be [itex]75\times 10^8[/itex] m/s but the answer key said [itex]57.0\times10^6 - 67\times10^6[/itex]m/s. What did I do wrong?
 
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Answers and Replies

  • #2
JSGandora
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Someone told me that the equation [itex] \lambda =\lambda_{0}\sqrt{{1-\beta}\over{1+\beta}} [/itex] 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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