Study Notes
Linear momentum is a vector quantity that is conserved over time in a closed system, meaning the total momentum remains constant if no external forces act on it.
- Linear Momentum — the product of an object's mass and velocity. Example: A car with mass 500 kg moving at 4 m/s has a momentum of 2000 kg·m/s.
- Principle of Conservation of Momentum — the total momentum of a system remains constant if no external forces act on it. Example: A swimmer diving off a boat causes the boat to move backward to conserve momentum.
- External Forces — forces acting from outside a system, like friction or weight. Example: Friction slowing down a moving car.
- Internal Forces — forces exchanged within a system, such as tension in a string. Example: Tension in a spring within a closed system.
- Elastic Collisions — collisions where kinetic energy is conserved. Example: Two billiard balls colliding and bouncing off each other.
- Inelastic Collisions — collisions where kinetic energy is not conserved and may convert to other forms like heat. Example: A car crash where the cars crumple and stick together.
Exam Tips
Key Definitions to Remember
- Linear Momentum: The product of mass and velocity.
- Principle of Conservation of Momentum: Total momentum remains constant in a closed system.
- Elastic Collision: A collision where kinetic energy is conserved.
- Inelastic Collision: A collision where kinetic energy is not conserved.
Common Confusions
- Confusing momentum with kinetic energy.
- Misunderstanding the difference between elastic and inelastic collisions.
Typical Exam Questions
- What is the principle of conservation of momentum? The total momentum of a system remains constant if no external forces act on it.
- How do you determine if a collision is elastic? Check if kinetic energy is conserved before and after the collision.
- What happens in a perfectly inelastic collision? Objects stick together, and kinetic energy is not conserved.
What Examiners Usually Test
- Ability to calculate momentum before and after collisions.
- Understanding of the difference between internal and external forces.
- Application of conservation of momentum in one and two-dimensional problems.