Doppler shift of an approaching source with interference problem

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Homework Help Overview

The problem involves the Doppler effect, specifically regarding a police car with a siren moving towards a warehouse and the frequency of sound reflected back to the car. The context is centered on understanding how the motion of the source and observer affects the perceived frequency.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of the Doppler shift formula for an approaching source and consider the implications of the warehouse reflecting sound waves. There is an exploration of how to treat the reflected waves and the roles of the source and observer in this scenario.

Discussion Status

Some participants have provided guidance on how to approach the problem, suggesting that the reflected waves can be treated with the source at rest and the observer moving towards it. There is an acknowledgment of successful attempts to apply these concepts, indicating a productive direction in the discussion.

Contextual Notes

There is a mention of the assumption that the warehouse reflects 100% of the incident waves, which may influence the interpretation of the problem. The original poster expresses uncertainty about the next steps after calculating the initial frequency shift.

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Homework Statement



P15. The police car with its 300 Hz siren is moving toward a warehouse at 30 m/s, intending to crash through the door. What frequency does the driver of the police car hear reflected from the warehouse? (5 marks)

Homework Equations


doppler shift for an approaching source. (f+) = fo / [1-vs/v]


The Attempt at a Solution



the doppler shift of the siren at the door is (300Hz)/ (1- [(30m/s)/(343m/s)]) =328.75Hz

now assume that the warehouse/ warehouse door reflects 100% of the incident waves.

I really have no idea where to go from here.
 
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For reflected waves, treat source at rest and the observer is moving towards the source with the velocity equal to the velocity of the police car.
 
The warehouse reflects each wave that hits it, and becomes a source.
The car is driving through the reflected waves.
 
hey guys thanks for the reply I tried it and it worked.
cheers
 

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