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1.3.1States of Matter

Momentum — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 24 of 30 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Momentum Basics

Momentum describes how much motion an object has, combining its mass and its velocity.

Momentum
  • Momentum The product of mass and velocity, calculated from p = mv and measured in kg m/s.
Vector quantity
  • Vector quantity Momentum has a direction, the same as the direction of the velocity.
Mass effect
  • Mass effect A heavier object moving at the same velocity has a larger momentum.
Velocity effect
  • Velocity effect A faster object of the same mass has a larger momentum than a slower one.
Sign convention
  • Sign convention Momentum in the opposite direction to the chosen positive direction is negative.

Part 2 of 5Conservation of Momentum

In a collision with no external forces, the total momentum before equals the total momentum after.

1
Choose a positive direction and assign signs to the velocities of each object.
2
Calculate the total momentum before the collision by adding the momenta of all objects.
3
Calculate the total momentum after the collision, using the new velocities.
4
Set the total before equal to the total after, and solve for the unknown velocity.

Part 3 of 5Types of Interaction

Types of Interaction
Stuck together
  • Stuck together After a collision where objects join, the combined mass moves with one common velocity.
Separate after
  • Separate after Objects that bounce apart each have their own velocity after the collision, but total momentum is still conserved.
Starting at rest
  • Starting at rest If the total momentum before is zero, the total momentum after is also zero, as in an explosion.
Closed system
  • Closed system Momentum is conserved only when no net external force acts on the system of objects.

Part 4 of 5Worked Example

Question

  • A 2 kg trolley moving at 3 m/s to the right collides with a 1 kg trolley at rest.
  • They stick together.
  • Calculate the velocity of the combined trolleys.

  1. Total momentum before = (2 × 3) + (1 × 0) = 6 kg m/s to the right.
  2. Total mass after = 2 + 1 = 3 kg.
  3. Total momentum after = 3 × v, so 3v = 6.
  4. v = 6 ÷ 3 = 2 m/s to the right.

Answer The combined trolleys move at 2 m/s to the right.

Part 5 of 5Exam Checklist & Tips

1.3.1 – Key Points for the Exam

  • Momentum The product of an object's mass and velocity, measured in kg m/s.
  • Conservation of momentum The principle that total momentum is unchanged in a closed system with no net external force.
  • Closed system A group of objects with no external forces acting on it.
  • Collision An interaction between objects in which they exert forces on each other.

Common Mistakes

  • Forgetting that momentum is a vector, so the direction of each velocity must be included.
  • Using speed instead of velocity when the objects move in opposite directions.
  • Applying conservation to each object separately, rather than to the total of all objects.
  • Using mass in grams without converting to kilograms before calculating momentum.

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