A motorist tried to defend a charge of driving through a red light on the grounds that the Doppler shift made it look green. Suggest why a good physics student would advise him against it.

Question

anonymous · Answer

The doppler shift equation is$$f=f_o[(c+v_r)/(c+v_s)]$$Taking the source as stationary and solving for the receiver's (driver's) speed. I get$$v_r=c[(f/f_o)-1]$$Remember that the frequency of red light is 440THz and green light is 560THz.
Do you think the resulting speed is within the speed limit?

anonymous · Answer

If you are using relativity, it is$$v_r=c[[(f/f_o)^2-1]/[(f/f_o)^2+1]]$$

aaronq · Answer

nevermind it being within the speed limit, he would be going at 25% of c ! lollll