Work, Energy, Power & Energy Transformations
Work done by a force, forms of energy, kinetic and gravitational potential energy, law of conservation of energy, power calculations, and renewable vs non-renewable energy in Ghana.
The Akosombo Dam converts gravitational potential energy of Lake Volta water into kinetic energy of rushing water through penstocks, turning hydro-turbines into mechanical rotational energy, which generators convert into electrical energy distributed by GRIDCo.
Key Syllabus Learning Objectives
- 1Define work, energy, and power with their respective SI units and formulas
- 2Derive and calculate Kinetic Energy (1/2 mv²) and Gravitational Potential Energy (mgh)
- 3Demonstrate the Law of Conservation of Energy for freely falling bodies and swinging pendulums
- 4Analyze renewable vs non-renewable energy sources and discuss Ghana’s renewable energy targets
Mechanical Energy Transformations & Conservation
- Simple Pendulum: At highest amplitude points, velocity = 0, so KE = 0 and PE is maximum. At equilibrium midpoint, height is minimum, so PE is minimum and KE (speed) is maximum.
- Rollercoaster / Free Fall: As an apple falls from a tree, its potential energy converts continuously into kinetic energy. Just before hitting the ground, all initial PE is converted into KE: v = √(2gh).
- Dissipation of Energy: In real systems, friction and air resistance convert some mechanical energy into non-recoverable thermal energy (heat) and sound.
Pounding fufu with a pestle involves lifting the wooden pestle (gaining PE = mgh) and accelerating it downward so that KE crushes cassava and plantain in the mortar.
The total mechanical energy remains conserved during free motion; potential energy lost equals kinetic energy gained.
Power & Electrical Energy Consumption in Ghana
- Kilowatt-hour (kWh): Commercial unit of electrical energy. 1 kWh = 1,000 W × 3,600 s = 3,600,000 Joules (3.6 MJ).
- Energy Efficiency: Energy rating labels (1 to 5 stars) on refrigerators and air conditioners in Ghana signify appliances that perform the same work while drawing less electric power.
Replacing incandescent filament lamps with modern LED bulbs reduces power demand from 60 W to 9 W, lowering monthly household ECG utility bills.
Commercial electricity meters measure total energy consumed in kilowatt-hours (kWh), not instantaneous power.
- Do not confuse power (Watts) with work/energy (Joules). Writing "Work done = 50 W" will cause you to forfeit the final mark.
- When using g in calculations, check the examination instructions: WAEC standard is g = 10 m/s² unless explicitly instructed to use 9.8 m/s².
- State formulas before substituting numbers: writing W = mgh or KE = 1/2 mv² secures the method mark (M1).
- Squaring both mass and velocity in KE = 1/2 mv² instead of squaring only the velocity.
- Assuming work is done when a porter carries a load on their head while walking horizontally at constant speed (force is vertical, motion is horizontal, angle θ = 90°, cos 90° = 0, so work done against gravity = 0).
- Confusing renewable energy with clean energy (biomass burning is renewable but produces smoke/carbon emissions).
- Can I calculate work done when a force acts at an angle to the displacement?
- Can I prove that v = √(2gh) for an object dropped from height h under gravity?
- Can I convert 5 kilowatt-hours into Joules?
- Can I list 3 advantages and 2 disadvantages of solar energy in Northern Ghana?
Ready for the Topic Quiz?
10 WAEC-standard multiple choice questions with instant explanations.
Student Study Notes & Discussion
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