---
title: "A small block of mass \\(m\\) is pressed against the rough vertical inner wall of a hollow cylinder of radius \\(R\\). The cylinder rotates about its vertical central axis at a constant angular speed \\(\\omega\\) such that the block remains at a constant height without sliding down the wall. Which of the following statements correctly identifies the horizontal force or forces acting on the block in an inertial reference frame and provides the valid physical justification?"
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url: "https://nerd-notes.com/ubq/120563/"
date_modified: "2026-08-23T04:41:38+00:00"
---

# A small block of mass \(m\) is pressed against the rough vertical inner wall of a hollow cylinder of radius \(R\). The cylinder rotates about its vertical central axis at a constant angular speed \(\omega\) such that the block remains at a constant height without sliding down the wall. Which of the following statements correctly identifies the horizontal force or forces acting on the block in an inertial reference frame and provides the valid physical justification?

A small block of mass \(m\) is pressed against the rough vertical inner wall of a hollow cylinder of radius \(R\). The cylinder rotates about its vertical central axis at a constant angular speed \(\omega\) such that the block remains at a constant height without sliding down the wall. Which of the following statements correctly identifies the horizontal force or forces acting on the block in an inertial reference frame and provides the valid physical justification?

![A vertical cylinder with radius \(R\) shown in perspective. A vertical dashed line represents the central axis of rotation with a curved arrow labeled \(\omega\) indicating rotation. A small rectangular block of mass \(m\) is in contact with the inner vertical right wall of the cylinder. A horizontal dashed line connects the central axis to the block, labeled \(R\). No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787460098-R2Wj5H.jpg)

- **A.** The horizontal forces are an inward normal force and an outward centrifugal force, because the block remains at a fixed distance from the rotation axis and is therefore in horizontal equilibrium.
- **B.** The only horizontal force is the normal force directed radially inward, because the block accelerates toward the central axis and this centripetal acceleration requires a net inward force supplied by a physical contact interaction.
- **C.** The only horizontal force is a static friction force directed radially inward, because static friction is required to keep the block moving along the circular path without slipping.
- **D.** The horizontal forces are the inward normal force and a distinct inward centripetal force, because the centripetal force is a separate physical contact force that acts alongside the normal force to maintain circular motion.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120563/*