How fast would a car need to travel to make a yellow light appear to be green as

Question

How fast would a car need to travel to make a yellow light appear to be green as the car approached an intersection? Would a judge accept the excuse of such a Doppler shift for running a yellow light?

PART 4:

In order to use the relation from Part 3 to find v, you need values for the source frequency fsource and the observer frequency fobs. What is a reasonable estimate for fsource? Hint: What is the frequency of yellow light?

What is a reasonable estimate for fobs? Hint: What is the frequency of green light?

Using the your values for fobs and fsource, what is the speed of the observer?

How fast would a car need to travel to make a yellow light appear to be green as the car approached an intersection? Would a judge accept the excuse of such a Doppler shift for running a yellow light? G Part 1-Recognize the Principles O Part 2- Sketch the Problem E Part 3 -Identify the Relationships In order to shift the color of the light from yellow to green, is the observer (the car) moving toward or away from the source of the light? The car is moving toward the traffic light O The car is moving away from the traffic light Good. Green light has a higher trequency than yellow light To shitt the trequency to a higher value, the observer must be moving toward the source. If the observer (the car) is moving toward the source of the light at a speed v, which relation gives the Doppler shift? Here fobs is the frequency seen by the observer and fsource is the frequency emitted by the source. 1+vfc 1- v/c obs source fobs source VV Good Part 4 . Solve Estimates In order to use the relation from Part 3 to find v, you need values for the source frequency fsource and the observer frequency fobs. What is a reasonable estimate for fsource? Hint: What is the frequency of yellow light? 510 Your value is a bit low You might want to consult one of the graphs showing the electromagnetic spectrum in your textbook. Haz What is a reasonable estimate for fobs? Hint: What is the frequency of green light? Hz Calculations (use your estimates) Using the your values for fobs and fsource, what is the speed of the observer? mis

Explanation / Answer

Part 4a

Here fsource is the frequency of light emitted by traffic signel.

fsource = fyellow light = 5.3×1014 Hz

fobs = freuency of green light = 5.66×1014 Hz

Part C

(fobs/fsource)2 = (1+V/c)/(1-V/c)

It gives V = 0.0656227×c = 0.0656227×3×108 m/sec

V = 1.97×107 m/sec

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