Doppler Effect for Sound
/A tutorial sheet on the Doppler effect for sound waves is given below.
- State a definition of the Doppler effect for sound waves.
- A train moves to the east at a speed v. The speed of sound in air is vs. The train emits sound waves. Find the speed of the sound waves (a) in front of the train, (b) behind the train
- A fire truck has a siren of frequency f. The truck moves at a constant velocity v relative to the ground. The speed of sound in air is vs. What is the frequency of the sound waves heard by a stationary observer as the truck approaches them?
- In question 2 does the frequency of the sound heard by the observer increase, stay the same or decrease as the fire truck approaches?
- A train has a whistle of frequency f that emits sound waves that travel through air at a speed vs. The train moves at a speed u to the east. A second train moves to the east at a speed v, where u is less than v. Is the frequency of the sound waves heard on the second train f(v - u)/vs?
A train has a whistle of frequency f that emits sound waves which travel through air at a speed vs. The train moves at a speed u towards a tunnel in a vertical mountain. Is the frequency of the reflected sound waves heard on the train 2fu/vs?
A physics student drops a vibrating 440 Hz tuning fork down an elevator shaft in a tall building. When the student hears a frequency of 400 Hz, how far has the tuning fork fallen? Take the speed of sound in air as 340 m s-1. (Tippler, Physics, second edition, p 483)
