---
title: "A small block of mass \\(m\\) moves along a horizontal, frictionless surface to the right with speed \\(v_0\\). It collides head-on and elastically with a large block of mass \\(M\\) that is moving to the left with speed \\(u_0\\). Which of the following statements correctly describes the final speed of the small block and the change in kinetic energy of the large block in the limiting case where \\(M \\gg m\\)?"
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url: "https://nerd-notes.com/ubq/120742/"
date_modified: "2026-08-23T04:42:56+00:00"
---

# A small block of mass \(m\) moves along a horizontal, frictionless surface to the right with speed \(v_0\). It collides head-on and elastically with a large block of mass \(M\) that is moving to the left with speed \(u_0\). Which of the following statements correctly describes the final speed of the small block and the change in kinetic energy of the large block in the limiting case where \(M \gg m\)?

A small block of mass \(m\) moves along a horizontal, frictionless surface to the right with speed \(v_0\). It collides head-on and elastically with a large block of mass \(M\) that is moving to the left with speed \(u_0\). Which of the following statements correctly describes the final speed of the small block and the change in kinetic energy of the large block in the limiting case where \(M \gg m\)?

![A horizontal straight line represents a flat surface. On the left side of the surface, a small square block is labeled m. A horizontal arrow pointing to the right extends from the right face of block m and is labeled v_0. On the right side of the surface, a large square block with twice the side length of block m is labeled M. A horizontal arrow pointing to the left extends from the left face of block M and is labeled u_0. Both blocks sit directly on the horizontal line with horizontal space between them. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787460176-teWNWx.jpg)

- **A.** The small block rebounds to the left with speed \(v_0\), and the kinetic energy of the large block does not change.
- **B.** The small block rebounds to the left with speed \(v_0 + u_0\), and the kinetic energy of the large block decreases by \(\dfrac{1}{2}m(v_0 + u_0)^2\).
- **C.** The small block rebounds to the left with speed \(v_0 + 2u_0\), and the kinetic energy of the large block does not change.
- **D.** The small block rebounds to the left with speed \(v_0 + 2u_0\), and the kinetic energy of the large block decreases by \(2m u_0(v_0 + u_0)\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120742/*