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## Homework Statement

A state trooper chases a speeder along a straight stretch of road; both vehicles move

at 160 km/h. The siren on the trooper's vehicle produces sound at a frequency of 500 Hz.

What is the Doppler shift in the frequency heard by the speeder?

## Homework Equations

This is what I need the answer to.

## The Attempt at a Solution

I understand why the answer is 500 Hz. They are both traveling at the velocity with respect to one another, so there is no doppler effect taking place---it is cancelled out by the equal velocity and direction of the vehicles. What I do not understand is, how do I prove it?

Thanks!