This chapter deals with the physical concepts of work done by a force, various forms of energy, conservation of energy, power, and collisions. These concepts are foundational for understanding both mechanics and real-world physical phenomena.
📚 Subtopics Covered:
- Work
- Kinetic Energy
- Work-Energy Theorem
- Potential Energy
- Conservative and Non-Conservative Forces
- Mechanical Energy Conservation
- Power
- Collisions
1️⃣ Work
✅ Definition:
Work is said to be done when a force is applied on a body and the body is displaced in the direction of the applied force.
🔣 Formula:
Where:
🔄 Types of Work:
🎯 Unit: Joule (J)
🧮 1 Joule = Work done when 1 N of force displaces a body by 1 m
2️⃣ Kinetic Energy (K.E.)
✅ Definition:
Kinetic Energy is the energy possessed by a body due to its motion.
🔣 Formula:
Where:
🎯 Unit: Joule (J)
📌 Note: A body at rest has zero kinetic energy.
3️⃣ Work-Energy Theorem
✅ Statement:
The net work done by all the forces acting on a body is equal to the change in its kinetic energy.
🔣 Expression:
4️⃣ Potential Energy (P.E.)
✅ Definition:
Potential Energy is the energy possessed by a body due to its position or configuration.
🔣 Formula (Gravitational P.E.):
5️⃣ Conservative & Non-Conservative Forces
🧲 Conservative Forces:
- Work done is path independent.
- Energy is conserved.
- Examples: Gravitational force, Spring force
🔥 Non-Conservative Forces:
- Work done depends on the path.
- Energy is not conserved (lost as heat, etc.)
- Examples: Friction, Air resistance
6️⃣ Conservation of Mechanical Energy
✅ Statement:
The total mechanical energy (sum of kinetic and potential energy) of a system remains constant if only conservative forces are acting.
🔣 Formula:
📌 Example:
A body falling freely from a height converts potential energy to kinetic energy, but total mechanical energy remains constant.
7️⃣ Power
✅ Definition:
Power is the rate of doing work or the rate of transfer of energy.
🔣 Formula:
🎯 Unit: Watt (W)
1 Watt = 1 Joule/second
💡 Other Units:
| Unit | Equivalent |
| Kilowatt | 1000 W |
| Horsepower | 746 W |
8️⃣ Collisions
✅ Types of Collisions:
| Type | Description | Momentum | Kinetic Energy |
| Elastic Collision | Both momentum and kinetic energy are conserved | ✔️ | ✔️ |
| Inelastic Collision | Only momentum is conserved, kinetic energy is not | ✔️ | ❌ |
| Perfectly Inelastic | Bodies stick together after collision | ✔️ | ❌ |
📌 Formulae in 1D Elastic Collision:
📊 Visual Recap
🖼️ Image Ideas for Notes (to include):
- Diagram of force and displacement at different angles
- Graph showing K.E. vs speed
- Pendulum illustrating conservation of mechanical energy
- Block sliding on an inclined plane (friction vs no friction)
- Power vs time bar graph
- Momentum and K.E. comparison in collisions
📝 Final Tips for NEET Aspirants:
- Focus on conceptual clarity of work and energy forms.
- Practice numericals based on work-energy theorem and power.
- Memorize formulae, but understand their derivations and conditions of applicability.
- Use previous year NEET questions to gauge difficulty and pattern.