---
title: "A train sounding its horn at a constant frequency moves at a constant speed directly toward a stationary observer standing on a platform. Which of the following claims correctly describes the pitch (frequency) heard by the observer compared to the emitted pitch, and provides the correct physical justification?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/117222/"
date_modified: "2026-08-04T06:45:02+00:00"
---

# A train sounding its horn at a constant frequency moves at a constant speed directly toward a stationary observer standing on a platform. Which of the following claims correctly describes the pitch (frequency) heard by the observer compared to the emitted pitch, and provides the correct physical justification?

A train sounding its horn at a constant frequency moves at a constant speed directly toward a stationary observer standing on a platform. Which of the following claims correctly describes the pitch (frequency) heard by the observer compared to the emitted pitch, and provides the correct physical justification?

- **A.** The observed pitch is lower than the emitted pitch because the wavefronts ahead of the train are stretched apart, increasing the observed wavelength.
- **B.** The observed pitch is higher than the emitted pitch because the wavefronts ahead of the train are compressed together, decreasing the observed wavelength.
- **C.** The observed pitch is higher than the emitted pitch because the speed of the sound waves through the air increases due to the forward motion of the train.
- **D.** The observed pitch is lower than the emitted pitch because the sound waves lose energy as they propagate through the air toward the observer.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117222/*