# Calculating Ambulance Frequency Change: -113 Hz

• Any Help
In summary, the frequency of the ambulance's siren is 880 Hz and it is traveling at a constant speed of 22 m/s. When it passes by you, the speed of sound is 343 m/s. The observed frequency of the siren changes by -113 Hz as it passes you due to the Doppler effect. This is because the frequency increases when the ambulance is moving towards you and decreases when it moves away from you. The correct equation to calculate this change is FL2-FL1=827-940=113 Hz.
Any Help

## Homework Statement

:
An ambulance has a siren of frequency 880 Hz. You are sitting at a stop light as the ambulance passes you, traveling at a constant 22 m/s. If the speed of sound is 343 m/s, what is the change in the frequency that you hear as the ambulance passes you?

• A

-53 Hz

• B

-60 Hz

• C

-56 Hz

• D

-113 Hz

• E

-116 Hz
the correct Answer is D : -113 Hz

## Homework Equations

WHERE FL and vL are the frequency and velocity of sound heard by the personL
fs and vs are the frequency and velocity of sound emmited by the source

## The Attempt at a Solution

using the equation we get FL=880x(343+0)/(343-22) therefore FL=940.3Hz
the difference is FL-Fs=940.3-880=60.311Hz
but its not correct.
the correct answer is -113Hz why?

What's the observed frequency when the ambulance is moving towards you? And then away from you?

Doc Al said:
WhaF frequency when the ambulance is moving towards you? And then away from you?
1) when towards me it is FL1=Fs*v/(v-vs)=880*343/(343-22)=940 Hz
when moves away from me FL2=Fs*v/(v+vs)=880*343/(343+22)=827Hz
FL2-FL1=827-940=113 Hz
Ah okay thanksssss

## What is the purpose of calculating ambulance frequency change?

The purpose of calculating ambulance frequency change is to determine the change in frequency of ambulance sirens as they move towards or away from a stationary observer. This can help determine the speed and direction of the ambulance.

## How is ambulance frequency change calculated?

Ambulance frequency change is calculated using the Doppler effect equation: Δf = (v/c)f, where Δf is the change in frequency, v is the velocity of the ambulance, c is the speed of sound, and f is the original frequency of the ambulance siren.

## What does a negative change in frequency (-113 Hz) mean in terms of ambulance movement?

A negative change in frequency (-113 Hz) means that the ambulance is moving away from the observer. This indicates that the ambulance is either slowing down or driving in the opposite direction of the observer.

## What factors can affect the accuracy of calculating ambulance frequency change?

Several factors can affect the accuracy of calculating ambulance frequency change, including the speed of the ambulance, the distance between the ambulance and the observer, and any obstacles or reflections that may alter the sound waves.

## How can calculating ambulance frequency change be useful in emergency situations?

Calculating ambulance frequency change can be useful in emergency situations as it can help determine the direction and speed of the ambulance. This information can be used to plan the quickest and safest route for the ambulance to reach its destination.

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