## College Physics (4th Edition)

A driver would have to drive with a speed of $5.66\times 10^7~m/s$ toward a red light in order to see it as green.
Let $\lambda_1 = 630~nm$ and let $\lambda_2 = 530~nm$ We can find the relative speed $v$: $\lambda_1 = \lambda_2~(1+\frac{v}{c})$ $\frac{v}{c}~\lambda_2 = \lambda_1 - \lambda_2$ $\frac{v}{c} = \frac{\lambda_1 - \lambda_2}{\lambda_2}$ $v = \frac{\lambda_1 - \lambda_2}{\lambda_2}~c$ $v = \left(\frac{630~nm - 530~nm}{530~nm}\right)~(3.0\times 10^8~m/s)$ $v = 5.66\times 10^7~m/s$ A driver would have to drive with a speed of $5.66\times 10^7~m/s$ toward a red light in order to see it as green.