Understanding Work, Energy, and Power in A Level Physics AS

Key Energy Concepts

This topic covers several forms of energy, including:

• Kinetic Energy - The energy possessed by an object due to its motion.
• Gravitational Potential Energy - The potential energy an object possesses due to its position in a gravitational field.
• Elastic Potential Energy - The potential energy stored in deformed elastic materials like springs.

The principle of conservation of energy states that total energy in an isolated system remains constant, with energy transforming from one form to another but never created or destroyed.

Work and the Work-Energy Theorem

Work is done when a force acts on an object, causing it to move in the direction of the force. The work-energy theorem relates the work done on an object to its change in kinetic energy.

For a constant force F applied over a displacement s, the work done is given by:

Work = F × s × cos(θ)

Where θ is the angle between the force and displacement vectors.

Worked Example

Problem: A 5 N force acts on a 2 kg object, causing it to move 3 m in the direction of the force. Calculate the work done.

Solution:

• Given: F = 5 N, m = 2 kg, s = 3 m, θ = 0° (force and displacement in same direction)
• Work = F × s × cos(θ) = 5 × 3 × cos(0°) = 15 J

Power and Efficiency

Power is the rate at which work is done or energy is transferred. It is calculated as:

Power = Work done / Time taken

Efficiency is a measure of how much useful work is extracted from the total energy input into a system. For example, a motor with an efficiency of 80% means that 20% of the input energy is wasted, typically as heat.

These concepts find applications in analyzing mechanical systems, energy transformations, and solving problems using energy methods in A Level Physics AS.

For more resources, refer to the OCR A Level Physics AS specification and relevant BBC Bitesize pages.