Two identical sirens sound, one on a parked car and one on a car speeding towards you. What differs?
AOnly the speeding siren is audible
BBoth are heard at the same pitch
CThe parked siren sounds higher
DThe speeding siren sounds higher
Answer & Solution
Correct answer: D. The speeding siren sounds higher
1. A stationary source sends the same wavelength to observers on every side.
2. A source moving towards you bunches its compressions closer together.
3. That shorter wavelength is received as a higher frequency, so a higher pitch.
4. Once it passes, the same siren drops to a lower pitch as the compressions spread out.
_Source: OpenStax Physics (high school, CC BY 4.0), Ch 14 "Sound", section 14.3 Doppler Effect and Sonic Booms_
Related questions
A singer's note makes a piano string sound without touching it. What is happening?Why does the speed of sound in a gas change with temperature?Sound reaches you faster through a steel rail than through the air. Why?A sound is described as periodic. What does that say about the particles of the medium?A vibrating guitar string makes a sound. What does it do to the surrounding air?Why can sound not travel across a vacuum?You drive an oscillating object far above its natural frequency. What happens to the ampliWhat is resonance?