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23 Nov 2019

A speeder is pulling directly away and increasing his distance from a police car that is moving at 26 m/s with respect to the ground. The radar gun in the police car emits an electromagnetic wave with a frequency of 6.6 x 109 Hz. The wave reflects from the speeder's car and returns to the police car, where its frequency is measured to be 230 Hz less than the emitted frequency. Find the speeder's speed with respect to the ground.

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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

A police car's radar gun emits microwaves with a frequency of f1= 7.50 GHz. The beam reflects from a speeding car, which is moving toward the police car at 48.0m/s with respect to the police car. The speeder's radar detector detects the microwave at a frequency f2. a) Which is larger f1 or f2? b) Find the frequency difference f2- f1.

Suppose that a police car on the highway is moving to the right at28 m/s, while a speeder is coming up from almost directly behind ata speed of 38 m/s, both speeds being with respect to the ground.The police officer aims a radar gun at the speeder. Assume that theelectromagnetic wave emitted by the radar gun has a frequency of7.00 109 Hz. Find the the difference between the frequency of thewave that returns to the police car after reflecting from thespeeder's car, and the original frequency emitted by the policecar.


This is what I have so far: (sqrt(3E8-10 - 10)/(3E8+10 + 10)) x 7E9

Police radar detects the speed of a car. Microwaves of a precisely known frequency are broadcast towards the car. The moving car reflects the microwaves with a doppler shift. The reflected waves are received and combined with an attenuated version of the transmitted wave. Beats occur between the two microwave signals. The beat frequency is measured. 

For an electromagnetic wave reflected back to its source from a mirror approaching at speed v, show that the reflected wave has a frequency. 

 

Where f is the source frequency.

 

 

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