---
title: "A stack of two blocks, consisting of Block 1 on top of Block 2, moves across a horizontal table at a constant velocity \\( \\vec{v} \\) to the right. There is no relative motion between the two blocks. Which of the following correctly describes the horizontal force of friction exerted on Block 1 by Block 2?"
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url: "https://nerd-notes.com/ubq/109784/"
date_modified: "2026-03-26T05:49:58+00:00"
---

# A stack of two blocks, consisting of Block 1 on top of Block 2, moves across a horizontal table at a constant velocity \( \vec{v} \) to the right. There is no relative motion between the two blocks. Which of the following correctly describes the horizontal force of friction exerted on Block 1 by Block 2?

A stack of two blocks, consisting of Block 1 on top of Block 2, moves across a horizontal table at a constant velocity \( \vec{v} \) to the right. There is no relative motion between the two blocks. Which of the following correctly describes the horizontal force of friction exerted on Block 1 by Block 2?

![A side-view diagram showing two rectangular blocks stacked on a horizontal surface. Block 1, the smaller block, is placed on top of Block 2, the larger block. A horizontal arrow labeled with the vector v points to the right, indicating the motion of the entire two-block system. The surface below Block 2 is represented by a long horizontal line.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1774504198-cnzV7y.jpg)

- **A.** The friction force is zero because Block 1 is moving at a constant velocity and requires no net horizontal force.
- **B.** The friction force is directed to the right because Block 2 must exert a force to overcome the inertia of Block 1 and keep it in motion.
- **C.** The friction force is directed to the left because friction always opposes the direction of an object's velocity.
- **D.** The friction force is directed to the right with a magnitude equal to \( \mu_s m_1 g \) because Block 1 is at rest relative to Block 2.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/109784/*