---
title: "A block of mass \\(M\\) is at rest on a rough horizontal surface. A student pulls the block with a horizontal force of magnitude \\(F_{pull}\\). The student performs three trials with three different values of \\(F_{pull}\\): \\(5 \\text{ N}\\), \\(10 \\text{ N}\\), and \\(15 \\text{ N}\\). In all three trials, the block remains at rest. Which of the following correctly ranks the magnitude of the friction force \\(f\\) exerted by the surface on the block for the three trials and provides a correct justification?"
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url: "https://nerd-notes.com/ubq/112815/"
date_modified: "2026-05-01T18:11:45+00:00"
---

# A block of mass \(M\) is at rest on a rough horizontal surface. A student pulls the block with a horizontal force of magnitude \(F_{pull}\). The student performs three trials with three different values of \(F_{pull}\): \(5 \text{ N}\), \(10 \text{ N}\), and \(15 \text{ N}\). In all three trials, the block remains at rest. Which of the following correctly ranks the magnitude of the friction force \(f\) exerted by the surface on the block for the three trials and provides a correct justification?

A block of mass \(M\) is at rest on a rough horizontal surface. A student pulls the block with a horizontal force of magnitude \(F_{pull}\). The student performs three trials with three different values of \(F_{pull}\): \(5 \text{ N}\), \(10 \text{ N}\), and \(15 \text{ N}\). In all three trials, the block remains at rest. Which of the following correctly ranks the magnitude of the friction force \(f\) exerted by the surface on the block for the three trials and provides a correct justification?

![A rectangular block of mass M sits on a flat horizontal line representing a floor. A horizontal arrow labeled F_pull points to the right from the center of the block. A second horizontal arrow labeled f points to the left, originating from the contact surface between the block and the floor.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1777659105-dENWaV.jpg)

- **A.** \(f_{15\text{N}} > f_{10\text{N}} > f_{5\text{N}}\) because the block remains in translational equilibrium, so the static friction force must increase to match the increasing pulling force.
- **B.** \(f_{15\text{N}} = f_{10\text{N}} = f_{5\text{N}}\) because the friction force depends only on the mass of the block and the coefficient of static friction, which do not change between trials.
- **C.** \(f_{15\text{N}} = f_{10\text{N}} = f_{5\text{N}}\) because the block is at rest in all three trials, meaning the net force on the block is zero in every case.
- **D.** \(f_{15\text{N}} < f_{10\text{N}} < f_{5\text{N}}\) because as the pulling force increases, the block is closer to sliding, which reduces the grip between the surfaces.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/112815/*