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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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