---
title: "A mass moving with a constant speed \\( u \\) encounters a rough surface and comes to a stop. The mass takes a time \\( t \\) to stop after encountering the rough surface. The coefficient of dynamic friction between the rough surface and the mass is \\( 0.40 \\). Which of the following expressions gives the initial speed \\( u \\)?"
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url: "https://nerd-notes.com/ubq/84543/"
date_modified: "2025-09-15T03:49:13+00:00"
---

# A mass moving with a constant speed \( u \) encounters a rough surface and comes to a stop. The mass takes a time \( t \) to stop after encountering the rough surface. The coefficient of dynamic friction between the rough surface and the mass is \( 0.40 \). Which of the following expressions gives the initial speed \( u \)?

A mass moving with a constant speed \( u \) encounters a rough surface and comes to a stop. The mass takes a time \( t \) to stop after encountering the rough surface. The coefficient of dynamic friction between the rough surface and the mass is \( 0.40 \). Which of the following expressions gives the initial speed \( u \)?

- **A.** \(0.2gt\)
- **B.** \(0.4gt\)
- **C.** \(gt\)
- **D.** \(2.5gt\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/84543/*