---
title: "A sound source emitting a wave of constant frequency \\(f_0\\) moves at a constant speed to the right along a straight line between two stationary observers. Observer 1 is located to the right of the source (ahead of its motion), and Observer 2 is located to the left of the source (behind its motion). Which of the following correctly compares the frequencies \\(f_1\\) and \\(f_2\\) detected by Observers 1 and 2 to \\(f_0\\), and provides the correct explanation?"
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url: "https://nerd-notes.com/ubq/117231/"
date_modified: "2026-08-04T06:45:03+00:00"
---

# A sound source emitting a wave of constant frequency \(f_0\) moves at a constant speed to the right along a straight line between two stationary observers. Observer 1 is located to the right of the source (ahead of its motion), and Observer 2 is located to the left of the source (behind its motion). Which of the following correctly compares the frequencies \(f_1\) and \(f_2\) detected by Observers 1 and 2 to \(f_0\), and provides the correct explanation?

A sound source emitting a wave of constant frequency \(f_0\) moves at a constant speed to the right along a straight line between two stationary observers. Observer 1 is located to the right of the source (ahead of its motion), and Observer 2 is located to the left of the source (behind its motion). Which of the following correctly compares the frequencies \(f_1\) and \(f_2\) detected by Observers 1 and 2 to \(f_0\), and provides the correct explanation?

![A horizontal line represents the ground. On the far left, a stick figure is labeled Observer 2. On the far right, a stick figure is labeled Observer 1. In the middle, a circular sound source has a horizontal arrow pointing to the right labeled v_s. No wave fronts, sound wave arcs, or other lines appear. No additional labels appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785825902-tlD8JA.jpg)

- **A.** \(f_1 > f_0\) and \(f_2 < f_0\), because wave fronts are compressed ahead of the moving source and spaced farther apart behind it.
- **B.** \(f_1 > f_0\) and \(f_2 < f_0\), because the speed of the sound wave relative to the ground is greater in front of the source than behind it.
- **C.** \(f_1 < f_0\) and \(f_2 > f_0\), because wave fronts are stretched out ahead of the moving source and compressed behind it.
- **D.** \(f_1 > f_0\) and \(f_2 > f_0\), because any relative motion between a sound source and an observer causes an increase in observed frequency.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117231/*