---
title: "Two pucks, \\(A\\) and \\(B\\), slide on a frictionless horizontal surface in the \\(xy\\)-plane.  Puck \\(A\\) has mass \\(m_A = 2.0\\text{ kg}\\) and initial velocity \\(\\vec{v}_{Ai} = (4.0\\hat{i})\\text{ m/s}\\), and puck \\(B\\) has mass \\(m_B = 1.0\\text{ kg}\\) and initial velocity \\(\\vec{v}_{Bi} = (3.0\\hat{j})\\text{ m/s}\\).  The pucks collide, and immediately after the collision puck \\(B\\) has velocity \\(\\vec{v}_{Bf} = (4.0\\hat{i} – 1.0\\hat{j})\\text{ m/s}\\).  Which row in the table correctly indicates how the kinetic energy of puck \\(B\\), the total kinetic energy of the two-puck system, and the speed of the center of mass of the system change as a result of the collision?  | | Kinetic Energy of Puck \\(B\\) | Total Kinetic Energy of System | Speed of Center of Mass | | :— | :— | :— | :— | | (A) | Decreases | Decreases | Decreases | | (B) | Decreases | Remains constant | Remains constant | | (C) | Increases | Increases | Remains constant | | (D) | Increases | Decreases | Remains constant |"
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url: "https://nerd-notes.com/ubq/124435/"
date_modified: "2026-09-28T14:05:30+00:00"
---

# Two pucks, \(A\) and \(B\), slide on a frictionless horizontal surface in the \(xy\)-plane.

Puck \(A\) has mass \(m_A = 2.0\text{ kg}\) and initial velocity \(\vec{v}_{Ai} = (4.0\hat{i})\text{ m/s}\), and puck \(B\) has mass \(m_B = 1.0\text{ kg}\) and initial velocity \(\vec{v}_{Bi} = (3.0\hat{j})\text{ m/s}\).

The pucks collide, and immediately after the collision puck \(B\) has velocity \(\vec{v}_{Bf} = (4.0\hat{i} – 1.0\hat{j})\text{ m/s}\).

Which row in the table correctly indicates how the kinetic energy of puck \(B\), the total kinetic energy of the two-puck system, and the speed of the center of mass of the system change as a result of the collision?

| | Kinetic Energy of Puck \(B\) | Total Kinetic Energy of System | Speed of Center of Mass |
| :— | :— | :— | :— |
| (A) | Decreases | Decreases | Decreases |
| (B) | Decreases | Remains constant | Remains constant |
| (C) | Increases | Increases | Remains constant |
| (D) | Increases | Decreases | Remains constant |

Two pucks, \(A\) and \(B\), slide on a frictionless horizontal surface in the \(xy\)-plane.

Puck \(A\) has mass \(m_A = 2.0\text{ kg}\) and initial velocity \(\vec{v}_{Ai} = (4.0\hat{i})\text{ m/s}\), and puck \(B\) has mass \(m_B = 1.0\text{ kg}\) and initial velocity \(\vec{v}_{Bi} = (3.0\hat{j})\text{ m/s}\).

The pucks collide, and immediately after the collision puck \(B\) has velocity \(\vec{v}_{Bf} = (4.0\hat{i} - 1.0\hat{j})\text{ m/s}\).

Which row in the table correctly indicates how the kinetic energy of puck \(B\), the total kinetic energy of the two-puck system, and the speed of the center of mass of the system change as a result of the collision?

| | Kinetic Energy of Puck \(B\) | Total Kinetic Energy of System | Speed of Center of Mass |
| :--- | :--- | :--- | :--- |
| (A) | Decreases | Decreases | Decreases |
| (B) | Decreases | Remains constant | Remains constant |
| (C) | Increases | Increases | Remains constant |
| (D) | Increases | Decreases | Remains constant |

- **A.** Row A
- **B.** Row B
- **C.** Row C
- **D.** Row D

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/124435/*