JEE Physics Notes: Work, Energy, and Power

Introduction

Work, Energy, and Power are fundamental concepts in mechanics. Work is the measure of energy transfer when a force is applied to an object, energy is the capacity to do work, and power is the rate of doing work. These concepts are crucial for solving problems in JEE Physics.

1. Work

• Definition: Work is said to be done when a force is applied to an object and the object displaces in the direction of the force.
• Formula: W = Fd cosθ, where W is work, F is force, d is displacement, and θ is the angle between force and displacement.
• Types of Work:
  • Positive Work: When force and displacement are in the same direction.
  • Negative Work: When force and displacement are in opposite directions.
  • Zero Work: When there is no displacement or force is perpendicular to displacement.

2. Energy

• Definition: The capacity of a body to perform work.
• Types of Energy:
  • Kinetic Energy: Energy due to motion, given by KE = 1/2 mv².
  • Potential Energy: Energy stored due to position, given by PE = mgh.
  • Mechanical Energy: The sum of kinetic and potential energy.
  • Chemical, Nuclear, and Thermal Energy: Other forms of energy used in different applications.

3. Work-Energy Theorem

• It states that the work done on an object is equal to its change in kinetic energy.
• Mathematically, W = ΔKE = KEf - KEi.

4. Power

• Definition: The rate at which work is done.
• Formula: P = W/t, where P is power, W is work done, and t is time.
• SI Unit: Watt (W).
• Other Units: Horsepower (1 HP = 746 W).
• Instantaneous Power: The power at any instant, given by P = Fv.

5. Conservation of Energy

• Energy can neither be created nor destroyed; it can only be transformed from one form to another.
• In an isolated system, total energy remains constant.
• Example: A freely falling body converts potential energy into kinetic energy.

6. Collisions

• Elastic Collision: Both momentum and kinetic energy are conserved.
• Inelastic Collision: Only momentum is conserved, but kinetic energy is not.
• Perfectly Inelastic Collision: Objects stick together after collision.

Conclusion

Work, Energy, and Power are interrelated concepts essential for understanding mechanics. Mastering these topics helps in solving various JEE-level physics problems effectively.