---
title: "A block of mass \\(m\\) rests on top of a larger block of mass \\(M\\), which in turn rests on a rough horizontal surface with coefficient of kinetic friction \\(\\mu\\). A horizontal pulling force of magnitude \\(F\\) is applied directly to the top block, causing both blocks to accelerate to the right together without the top block slipping. What is the magnitude of the horizontal contact force exerted by the lower block on the upper block?"
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url: "https://nerd-notes.com/ubq/124015/"
date_modified: "2026-09-28T13:30:12+00:00"
---

# A block of mass \(m\) rests on top of a larger block of mass \(M\), which in turn rests on a rough horizontal surface with coefficient of kinetic friction \(\mu\). A horizontal pulling force of magnitude \(F\) is applied directly to the top block, causing both blocks to accelerate to the right together without the top block slipping. What is the magnitude of the horizontal contact force exerted by the lower block on the upper block?

A block of mass \(m\) rests on top of a larger block of mass \(M\), which in turn rests on a rough horizontal surface with coefficient of kinetic friction \(\mu\). A horizontal pulling force of magnitude \(F\) is applied directly to the top block, causing both blocks to accelerate to the right together without the top block slipping. What is the magnitude of the horizontal contact force exerted by the lower block on the upper block?

![A horizontal ground surface is represented by a solid horizontal line with diagonal hatching underneath. Resting on the ground is a rectangular block with mass labeled \(M\). Resting centered on top of block \(M\) is a smaller rectangular block with mass labeled \(m\). A single horizontal arrow labeled \(F\) points to the right, with its tail starting at the right vertical face of block \(m\). A label \(\mu\) is placed immediately below the ground line near the bottom-left of block \(M\). No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790602212-dxAxf2.jpg)

- **A.** \(\dfrac{m}{M + m}F - \mu m g\)
- **B.** \(\dfrac{M}{M + m}\left(F - \mu(M + m)g\right)\)
- **C.** \(\dfrac{M}{M + m}F - \mu m g\)
- **D.** \(\dfrac{M}{M + m}F + \mu m g\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/124015/*