Cambridge IGCSE 0625 · Topic 3 of 10

Energy, work, power and pressure

Energy stores and transfers, kinetic and potential energy, work, power, efficiency, energy resources and pressure.

📌 Key points

Energy stores include kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal).
Energy is transferred by forces (mechanical work), electrical currents, heating, and waves. Energy is conserved: it cannot be created or destroyed.
In every real transfer some energy is dissipated, usually by heating the surroundings.
Kinetic energy Eₖ = 12mv². Change in gravitational potential energy ΔEₚ = mgΔh.
Work done = force × distance moved in the direction of the force, W = Fd = ΔE. Work is measured in joules.
Power = work donetime taken = energy transferredtime taken. 1 W = 1 J/s.
Efficiency = useful energy outputtotal energy input × 100% (or the same with powers).
Renewable resources: solar, wind, hydroelectric, tidal, waves, geothermal, biofuels. Non-renewable: fossil fuels and nuclear fuel. The Sun is the source of all of them except geothermal, nuclear and tidal.
Pressure = forcearea, p = FA, in pascals (1 Pa = 1 N/m²). In a liquid, pressure increases with depth and density: Δp = ρgΔh.

Work done: Force × distance moved in the direction of the force.
Power: Work done (or energy transferred) per unit time.
Efficiency: Useful energy output ÷ total energy input, often as a percentage.
Kinetic energy: Energy stored in a moving object.
Gravitational potential energy: Energy stored because of an object’s height in a gravitational field.
Renewable resource: An energy resource that is not used up, because it is replaced naturally.
Pressure: Force per unit area.

A 0.50 kg ball is dropped from a height of 3.2 m. Ignoring air resistance, find its speed just before it hits the ground. (g = 9.8 m/s²)

💡 Exam tip

In Eₖ = 12mv² only the speed is squared: square v first, then multiply by m and halve.

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