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## Homework Statement

A speeder is pulling directly AWAY and INCREASING his distance from a police car that is moving at 27 m/s with respect to the ground. The radar gun in the police car emits an electromagnetic wave with a frequency of 7.2 x 109 Hz. The wave reflects from the speeder's car and returns to the police car, where its frequency is measured to be 310 Hz less than the emitted frequency. Find the speeder's speed with respect to the ground.

## Homework Equations

WHAT do I do with the answer that I get for relative velocity?

DO I subtract the 27 m/s from the 12.92 that I got as an answer??

## The Attempt at a Solution

fo=fs (1+Vrel/c)

Then I rearranged the equation to solve for the relative velocity.

I got: [(Change in frequency)/fs] * speed of light = relative velocity

which is 310 Hz/7.2E9 *3E8 = 12.92