# Easy/fustrating doppler queston - rather

In summary, the question is asking for the speed and crest spacing of a swimming duck in a pond with surface waves of known speed. The duck is the source of the waves and is moving at a constant speed. The frequency of the waves is 0.7142 Hz and the speed of the waves is 0.31 m/s. By determining the reference frame of the observer, the speed of the duck and the spacing of the crests behind the duck can be calculated.
Easy/fustrating doppler question - rather urgent

## Homework Statement

A swimming duck paddles the water with its feet once per time interval of 1.4 , producing surface waves with this period. The duck is moving at constant speed in a pond where the speed of surface waves is 0.31 , and the crests of the waves ahead of the duck have a spacing of 0.20 .

a)What is the duck's speed?
b)How far apart are the crests behind the duck?

## Homework Equations

f_d = f_s (v + v_d)/(v + v_s)

## The Attempt at a Solution

There are two things that I don't get. Is the duck the source or the detector of the waves? I think the duck is the source. Then f_s = 1/1.4 = 0.7142Hz
The waves in the front will have f_d = 0.31/0.2 = 1.55Hz and v_d = 0.31m/s
But what is the regular speed of the wave, v? Don't I ned that to solve for v_s?

First, yes, the duck is the source because it's generating the waves. However, you've confused some variables. 0.31 m/s is not v_d; the question states that 0.31 m/s is the speed of the waves. v_d is the speed of the person watching the duck with respect to the medium, the water.

So in the first part, I am looking for V_s. How do I find out what v_d and v are then?

v is the speed of the waves. The question tells you that it's 0.31 m/s. If you didn't know this, why did you do f_d = 0.31/0.2 = 1.55Hz? (It's correct, but I'm wondering how you got that if you didn't know the speed of the waves.)

The question doesn't explicitly say what v_d is, but you implicitly picked a reference frame by calculating f_d as 0.31/0.2. There's only one reference frame where the wave travels at 0.31 m/s. What's v_d in this frame?

## 1. What is the Doppler effect?

The Doppler effect is the change in frequency or wavelength of a wave as it moves relative to an observer. This can occur with all types of waves, including sound and light.

## 2. How does the Doppler effect affect sound?

The Doppler effect can cause the frequency of sound waves to appear higher or lower to an observer depending on their relative motion. This is why a siren on a moving vehicle will sound higher in pitch as it approaches and lower in pitch as it moves away.

## 3. What is an easy way to understand the Doppler effect?

An easy way to understand the Doppler effect is to think of it like a car passing by. As the car approaches, the frequency of the sound of its engine will seem higher, but as it moves away, the frequency will seem lower. This is because the sound waves are being compressed or stretched as the car moves.

## 4. Can the Doppler effect be applied to light waves?

Yes, the Doppler effect can also be applied to light waves. This is known as the Doppler shift and is used in astronomy to determine the speed and direction of celestial objects.

## 5. Is the Doppler effect always observed in real-life situations?

Yes, the Doppler effect is observed in many real-life situations, such as the sound of a passing train or the changing pitch of a passing ambulance siren. However, in some cases, the effect may be too small to be noticeable to the human ear.

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