1.7 ENERGY, WORK AND POWER (0625 Physics Syllabus)

Definitions:

• Work: Work is done when a force is applied to an object and the object moves in the direction of the force.

• Energy: The capacity to do work.

• Kinetic Energy: The energy of a body due to its motion.

• Potential Energy: The stored energy of a body due to its position or configuration.

• Power: The rate of doing work or the rate of energy transfer.

Formulas:

• Work (W) = Force (F) × Distance (d) × cos(θ)

• Kinetic Energy (KE) = 1/2 × m × v²

• Potential Energy (PE) = m × g × h

• Power (P) = Work done (W) ÷ Time (t)

• Efficiency = (Useful Energy Output ÷ Total Energy Input) × 100%

Key Notes:

• Work is only done if there is movement in the direction of the applied force.

• Energy can neither be created nor destroyed; it can only change form (Law of Conservation of Energy).

• Power measures how quickly work is done.

• Machines are never 100% efficient because some energy is always lost as heat or sound.

Worked Examples:

1. Work Done A force of 100 N moves an object 5 m in the same direction. W = F × d = 100 × 5 = 500 J

2. Kinetic Energy A 2 kg ball moves at 3 m/s. KE = 1/2 × m × v² = 0.5 × 2 × 3² = 9 J

3. Potential Energy A 5 kg object is raised to a height of 4m PE = m × g × h = 5 × 9.8 × 4 = 196 J

4. Power A machine does 2000 J of useful work in 50s P = W ÷ t = 2000 ÷ 50 = 40 W

5. Efficiency A machine takes 500 J of input energy but gives 400 J as useful output. Efficiency = (400 ÷ 500) × 100% = 80%

Illustrations (for diagrams):

Summary:

Work, energy, and power are closely related concepts.

• Work is done when a force causes displacement.

• Energy is the ability to do work.

• Power is how fast work is done.

Made by Hiba Shakeel

Curated by Yassein