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Thermodynamics and Elastic Collisions: Conservation of Momentum

Chloe Sanchez

Chloe Sanchez

8 min read

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Study Guide Overview

This study guide covers collisions in AP Physics 2, focusing on momentum and kinetic energy. It explains the conservation of momentum principle and details elastic and inelastic collisions. Key concepts include calculating final velocities, analyzing 2D collisions, and connecting collisions to thermodynamics. The guide provides example problems, common mistakes, exam tips, and practice questions with a scoring rubric.

Collisions: A Deep Dive 💥

Let's break down collisions, a key topic in AP Physics 2. Remember, collisions involve objects interacting and exchanging energy and momentum. Whether it's a gentle bump or a massive crash, understanding these interactions is crucial.

Conservation of Momentum

First things first: Momentum is King! 👑

  • If the net external force on a system is zero (or negligibly small), the total momentum of the system is conserved. This means the total momentum before a collision equals the total momentum after the collision.
  • Think of it like this: what goes in, must come out (in terms of total momentum).
  • Momentum is a vector, so consider direction.

Types of Collisions

Collisions come in two main flavors:

  • Elastic Collisions 🏀
    • Both momentum and kinetic energy (KE) are conserved. Think of perfectly bouncy objects.
    • Objects bounce off each other without losing any energy to heat or sound.
Key Concept

Key Point: KEi = KEf

Memory Aid

Memory Aid: Elastic = Energy is like a rubber band, it bounces back.

* Example: Imagine billiard balls colliding; they mostly retain their kinetic energy.
  • Inelastic Collisions 🧽
    • Momentum is conserved, but kinetic energy is NOT. Some KE is converted into other forms of energy (heat, sound, deformation).
    • Objects may stick together or deform.
Key Concept

Key Point: KEi ≠ KEf

Memory Aid

Memory Aid: Inelastic = Energy is lost like a sponge absorbing water.

* Example: A car crash; lots of energy is lost to deformation and heat.

Elastic Collisions: The Details

Key Principles

  • Conservation of Kinetic Energy: The total kinetic energy of the system remains constant. This means: KEinitial = KEfinal
  • Conservation of Momentum: The total momentum of the system remains constant. This means: pinitial = pfinal

Solving Elastic Collision Problems

  1. Identify: Determine if the collision is elastic. Look for keywords like "perfectly elastic" or if the prob...