Doppler effect with moving source and observer

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Homework Help Overview

The problem involves the Doppler effect, specifically with a moving source (an ambulance) and a moving observer (a driver). The scenario describes the change in frequency of a siren as the ambulance approaches and then passes the observer, with specific frequencies given for each phase.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of the Doppler effect equation and express confusion regarding the frequencies provided, particularly the distinction between emitted and observed frequencies. There is mention of needing a second equation to assist in solving the problem.

Discussion Status

The discussion is ongoing, with participants exploring the relationships between the frequencies and the speeds involved. Some guidance has been offered regarding the use of multiple equations, but no consensus or resolution has been reached yet.

Contextual Notes

Participants note the lack of the source frequency and the implications this has on their ability to solve the problem. The context of the problem is framed within a homework assignment, which may impose certain constraints on the discussion.

hopelessphysics
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Homework Statement


As you drive at a speed of 15.0 m/s an ambulance approaches you from behind with its siren blaring at a frequency of 1022 Hz. After the ambulance has passed you the signal is now 981 Hz. If both you and the ambulance travel at a constant speed how fast was the ambulance traveling?

Homework Equations


fo=fs(1+- vo/v)/(1+-vs/v)

The Attempt at a Solution


So I tried to use the equation above by plugging in the frequencies, but was trapped because the frequencies show only what the source was emitting, and not what the observer was hearing.
 
Last edited by a moderator:
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fo is the observer frequency.
You don't have the source frequency, but you have a second equation you can use.
 
What is the second equation?
 
The ambulance before and after it passes you => 2 equations
 

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