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Worksheet: Doppler Shift

Q1:

The graphs show the change in frequency with time of the sound of the horn of a fast-moving car that is heard by a person walking slowly by the side of the road as the car approaches and passes them. Which of the graphs (A), (B), (C), and (D) most correctly shows the changes in frequency that the pedestrian hears?

  • A(C)
  • B(A)
  • C(D)
  • D(B)

Q2:

Which of the following combinations of motion of a sound wave source and a sound wave observer produces the largest Doppler shift of the frequency of the wave as measured by the observer?

  • AAn observer moves toward a stationary sound wave source at 30 m/s.
  • BA sound wave source moves toward a stationary observer at 25 m/s.
  • CA sound wave source moves at 15 m/s toward an observer moving in the opposite direction to the sound wave source at 20 m/s.
  • D A sound wave source moves at 20 m/s away from an observer moving in the opposite direction to the sound wave source at 20 m/s.
  • EA sound wave source moves at 30 m/s in the same direction as an observer moving at 20 m/s.

Q3:

Which of the following combinations of motion of a sound wave source and a sound wave observer does not result in the observer measuring a different frequency of the sound wave to the frequency of the sound wave as measured at the source? Assume that all motion of sound wave sources and observers are at the same speed.

  • AAn observer moves toward a stationary sound wave source.
  • BA sound wave source moves toward a stationary observer.
  • CA sound wave source moves toward an observer moving in the opposite direction to the sound wave source.
  • DA sound wave source moves in the same direction as a moving observer.
  • EA sound wave source moves away from an observer moving in the opposite direction to the sound wave source.

Q4:

A firework is set up to launch horizontally in a fireworks display. As the firework’s fuse burns, it emits sound waves that have a frequency of 100 Hz and a wavelength of 3 m. When the rocket launches, it accelerates in a negligible time to a constant speed of 225 m/s and continues to emit sound waves with the same frequency and wavelength as before the launch, as shown in the diagram. An unwary person accidentally enters the firework display area and the firework travels directly toward them. The person is not moving.

According to the person, at what speed do wave fronts emitted from the rocket before it is launched travel?

According to the person, at what speed do wave fronts emitted from the flying rocket travel before the rocket reaches the point where the person stands?

The person manages to duck and avoid being hit by the firework, which then moves directly away from the person. According to the person, at what speed do wave fronts emitted from the rocket after it passes the person travel?

What is the frequency of the sound of the approaching firework as heard by the person?

What is the frequency of the sound of the receding firework as heard by the person?