• Frozen_Mind
In summary: The first time for when the screen is stationary and the second time for when the screen is moving. f3 = f2 Vs/(Vs + or - Vo), f3 = f2(1 + or - Vo/Vs)
Frozen_Mind
1. The problem statement
1) A train whistle has a frequency of 1000 Hz. If the train is speeding
at a velocity of 60 km/h past a stationary railroad crossing
attendant, what is the apparent frequency a) as the train approaches him, b) as it moves away from him?
Assume speed of sound to be 350 m/s.

2) A second train is approaching the first train (above) with a speed of
60 km/h. Obtain the frequency of the whistle of the first as heard by
the engineer of the second train.

3) Sound is reflected by a screen moving with a speed 20 km/h toward
the source and observer. If the frequency of the source is 450 khz,
what is the apparent frequency of the reflected sound?

## Homework Equations

f2 = f1Vs/(Vs + or - Vo), f2 = f1(1 + or - Vo/Vs)

meh I'm really not that quite sure :S

## The Attempt at a Solution

I could calculate number 1 using the doppler effect equation f2 = f1Vs/(Vs + or - Vo), but I'm not quite sure how to solve for number 2 and 3... help please ?

i think (not 100% sure) for part 2 and 3 you can use the same method as part 1 except the velocity will be the sum of the 2. so for part 2 the total velocity will be 60 + 60 = 120 km/h

Frozen_Mind said:

## Homework Equations

f2 = f1Vs/(Vs + or - Vo), f2 = f1(1 + or - Vo/Vs)
What do Vs and Vo mean?

Look up the Doppler formula for sound. There's a formula for when the source is moving and another for when the observer is moving. Of course you can combine them into a single formula when both are moving.

Pheo1986 said:
i think (not 100% sure) for part 2 and 3 you can use the same method as part 1 except the velocity will be the sum of the 2. so for part 2 the total velocity will be 60 + 60 = 120 km/h
No, that's not the right way to solve part 2. Instead you must combine the effect of a moving source (Vs) and a moving observer (Vo) using the complete Doppler formula.

For part 3, the reflecting screen becomes the source. Apply the Doppler formula twice.

## 1. What is the Doppler effect?

The Doppler effect is a phenomenon where the frequency of a sound wave appears to change when the source of the sound is moving relative to the observer.

## 2. What is the difference between the Doppler effect and the Advanced Doppler effect?

The Advanced Doppler effect takes into account the relative motion of both the source and the observer, while the regular Doppler effect only considers the motion of the source.

## 3. How does the Advanced Doppler effect affect light waves?

The Advanced Doppler effect can also be applied to light waves, where the frequency and wavelength of the light wave appear to change based on the relative motion of the source and observer.

## 4. What are some real-life applications of the Advanced Doppler effect?

The Advanced Doppler effect is used in many areas, such as astronomy to measure the speed and distance of stars, in weather forecasting to track the movement of storms, and in medical imaging to measure blood flow and heart rate.

## 5. Can the Advanced Doppler effect be used to measure the speed of objects in space?

Yes, the Advanced Doppler effect is commonly used in astronomy to measure the speed and direction of objects in space, such as stars, galaxies, and planets.

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