---
title: "Two skaters, Skater 1 of mass \\(m_1\\) and Skater 2 of mass \\(m_2\\), stand facing each other at rest on a horizontal, frictionless ice surface. Skater 1 pushes against Skater 2, causing both skaters to move away from each other in opposite directions. For the system consisting of both skaters, which of the following correctly identifies the net external horizontal force \\(\\Sigma F_{\\text{ext}}\\) acting on the system during the push and the change in the total kinetic energy \\(\\Delta K\\) of the system?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/120735/"
date_modified: "2026-08-23T04:42:55+00:00"
---

# Two skaters, Skater 1 of mass \(m_1\) and Skater 2 of mass \(m_2\), stand facing each other at rest on a horizontal, frictionless ice surface. Skater 1 pushes against Skater 2, causing both skaters to move away from each other in opposite directions. For the system consisting of both skaters, which of the following correctly identifies the net external horizontal force \(\Sigma F_{\text{ext}}\) acting on the system during the push and the change in the total kinetic energy \(\Delta K\) of the system?

Two skaters, Skater 1 of mass \(m_1\) and Skater 2 of mass \(m_2\), stand facing each other at rest on a horizontal, frictionless ice surface. Skater 1 pushes against Skater 2, causing both skaters to move away from each other in opposite directions. For the system consisting of both skaters, which of the following correctly identifies the net external horizontal force \(\Sigma F_{\text{ext}}\) acting on the system during the push and the change in the total kinetic energy \(\Delta K\) of the system?

![A side-view diagram of two skaters on a flat horizontal surface. A horizontal solid line represents the frictionless ice surface. On the left side of the center, a simple rectangular block is labeled \(m_1\). On the right side of the center, a second rectangular block is labeled \(m_2\). The two blocks are in contact at the vertical center line. A horizontal coordinate arrow labeled \(+x\) points to the right below the ground line. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787460175-7bkIkD.jpg)

- **A.** \(\Sigma F_{\text{ext}} \ne 0\), and \(\Delta K > 0\)
- **B.** \(\Sigma F_{\text{ext}} = 0\), and \(\Delta K > 0\)
- **C.** \(\Sigma F_{\text{ext}} = 0\), and \(\Delta K = 0\)
- **D.** \(\Sigma F_{\text{ext}} \ne 0\), and \(\Delta K = 0\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120735/*