Composition and Resolution of Forces Using Cosine and Sine Laws

Grade 11 · Physics

Semester 1 | Period 2 | Week 8

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Subject: Physics

Semester: 1

Period: 2

Week: 8

School Name:

Teacher’s Name:

Subject: Physics

Grade Level: Grade 11

Week & Period: Week 8, Period II

Date:

Sub-topic: Composition and Resolution of Forces Using Cosine and Sine Laws

Learning Objectives

By the end of this lesson, learners should be able to:

  1. Use the cosine law to calculate the magnitude of the resultant force.
  2. Use the sine law to calculate the direction of the resultant force.
  3. Resolve forces into components along given axes.

 

Previous Knowledge

Students should know basic trigonometry (sine, cosine laws) and vector components.

 

Instructional Materials

  • Protractors
  • Rulers
  • Calculators
  • Whiteboard

 

Anticipation (Warm-Up) – 5 minutes

Ask:

  • “How do we find unknown sides or angles in force triangles?”
  • Review sine and cosine laws.

 

Building Knowledge (Main Lesson) – 25 minutes

Learners’ Activities

  • Solve vector triangles using sine and cosine laws.
  • Practice resolving forces into components with different angles.

 

Consolidation (Review and Assessment) – 10 minutes

Oral Questions:

  • State the cosine and sine laws.
  • Calculate the components of a 100 N force acting at 30°.
  • Find the magnitude and direction of resultant force for two forces of 40 N and 50 N at 90°.

 

Homework / Assignment

  • Two forces of 70 N and 90 N act at 45°. Calculate resultant and angle with 70 N force.
  • Resolve a force of 150 N acting at 60° into horizontal and vertical components.

 

Notes – Detailed and Explained

  • Cosine law applies when you know two sides and included angle or all three sides.
  • Sine law helps find unknown angles or sides in oblique triangles.
  • Force resolution simplifies analysis by dealing with components.

 

Expanded Notes / Instructions

  • Use diagrammatic approaches alongside formulas.
  • Provide guided examples before independent practice.

 

Inclusive / Differentiation

  • Use physical models to illustrate vector triangles.
  • Break down problems into manageable steps.

 

Teacher’s Reflection

  • Did learners successfully apply sine and cosine laws?
  • Was force resolution clearly understood?