What is the difference between energy, work, and power in Physics?

In Physics, energy is the capacity to do work. Work is done when a force causes an object to move in the direction of the force. Power is the rate at which work is done or energy is transferred. These concepts are fundamental in the Cambridge IGCSE Physics curriculum under the topic of Motion, Forces and Energy.

How is work calculated in Physics?

Work is calculated using the formula: Work = Force x Distance x cos(θ), where Force is the applied force, Distance is the distance moved by the object in the direction of the force, and θ is the angle between the force and the direction of motion. This formula is essential for understanding work in the context of the Cambridge IGCSE Physics syllabus.

What are the different forms of energy covered in the Cambridge IGCSE Physics curriculum?

The Cambridge IGCSE Physics curriculum covers various forms of energy, including kinetic energy, potential energy, thermal energy, chemical energy, electrical energy, and nuclear energy. Each form of energy plays a crucial role in different physical processes and is a key part of understanding the topic of Energy, Work and Power.

How is power related to energy and work in Physics?

Power is the rate at which work is done or energy is transferred. It is calculated using the formula: Power = Work / Time or Power = Energy / Time. Power is measured in watts (W), where one watt equals one joule per second. Understanding power is important for analyzing how quickly energy is used or work is performed, as taught in the Cambridge IGCSE Physics course.

Why is understanding energy efficiency important in Physics?

Understanding energy efficiency is crucial because it helps us determine how effectively energy is converted from one form to another. Energy efficiency is calculated as the ratio of useful energy output to total energy input, expressed as a percentage. This concept is important in the Cambridge IGCSE Physics curriculum as it relates to real-world applications, such as reducing energy waste and improving the performance of machines and systems.

Why is "Using slope distance for $h$ in $mgh$" a common mistake in Energy, Work and Power?

Why it happens: Substituting whatever distance the question quotes. How to avoid it: h is the VERTICAL height change. For a ramp, use h = L . Source: 0625/42 — recurring

Why is "Forgetting to square velocity in KE" a common mistake in Energy, Work and Power?

Why it happens: Speed. How to avoid it: E_k = 1/2 m v^2 — the v is squared.

Why is "Quoting power in joules" a common mistake in Energy, Work and Power?

Why it happens: Confusing energy with power. How to avoid it: Power = energy / time, units watts (W) = J/s.

Why is "Getting an efficiency > 100%" a common mistake in Energy, Work and Power?

Why it happens: Inverting numerator and denominator. How to avoid it: Useful out goes ON TOP, total in goes UNDERNEATH. Always between 0 and 100%.

Why is "Confusing a solar cell with a solar panel" a common mistake in Energy, Work and Power?

Why it happens: Both sit on roofs and both use sunlight. How to avoid it: A solar cell uses light from the Sun to generate electricity directly. A solar panel uses infrared and other waves from the Sun to heat water. Source: 0625 — recurring

Why is "Saying tidal power comes from the Sun" a common mistake in Energy, Work and Power?

Why it happens: Assuming all water-based resources are solar. How to avoid it: Tides are caused mainly by the Moon's gravity, so tidal is one of the three resources (with geothermal and nuclear) that do NOT come from the Sun. Waves and hydroelectric DO come from the Sun.

Motion, Forces and EnergyCambridge IGCSE Physics (0625)

Energy, Work and Power

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Energy, Work and Power — Cambridge IGCSE 0625 Physics Extended (2026)

Forms of energy, conservation, KE and GPE formulas, $W = Fd$ , $P = E/t$ and efficiency. Cambridge expects clear before/after energy bookkeeping.

What you’ll learn

Mapped to the Cambridge IGCSE 0625 syllabus (2026-2028).

1.7 — State the principle of conservation of energy.
1.7 — Calculate kinetic and gravitational potential energy.
1.7 — Calculate work done using $W = Fd$ .
1.7 — Calculate power using $P = E/t$ .
1.7 — Calculate efficiency.
1.7.3 — Describe how useful energy is obtained, or electrical power generated, from the major energy resources, and their advantages and disadvantages.
1.7.3 — Know that radiation from the Sun is the main source of energy for most resources, and that energy is released by nuclear fusion in the Sun.

Energy and conservation

Energy never destroyed; just changes form. Track every joule.

Forms of energy to recognise:

Kinetic — motion.
Gravitational potential — height in a gravitational field.
Elastic — stretched or compressed material.
Chemical — bonds in food, fuel, batteries.
Thermal (internal) — random motion of particles.
Nuclear — bonds in nuclei.
Electrical — charges in motion.
Light, sound — radiated.

Conservation of energy. In a closed system, total energy is constant. It just transfers between forms.

Worked. A ball dropped from $5\,\text{m}$ .

Top: GPE = $mgh$ . KE = 0.
Just before hitting: GPE → 0. KE = original GPE.
Velocity from $\dfrac{1}{2}mv^{2} = mgh$ : $v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 5} \approx 9.9\,\text{m/s}$ .

Sankey diagram. Visualises energy transfers; total in $=$ total out (useful + wasted).

Arrow widths are proportional to energy; the input always equals useful output plus wasted energy.

Energy is conserved — total constant.
Track each form: KE, GPE, etc.
Use Sankey diagram for transfers.
Useful + wasted = total input.

Kinetic energy and gravitational potential energy

$\text{KE} = \frac{1}{2}mv^{2}$ , $\Delta \text{GPE} = mg\Delta h$ .

Kinetic energy. $\text{KE} = \dfrac{1}{2}mv^{2}.$

Speed has more impact than mass: doubling $v$ quadruples KE.

Worked. A $1500\,\text{kg}$ car at $20\,\text{m/s}$ .

$\text{KE} = \dfrac{1}{2} \times 1500 \times 400 = 300{,}000\,\text{J} = 300\,\text{kJ}$ .

Gravitational potential energy. $\Delta \text{GPE} = mg\Delta h.$

The $\Delta$ matters — GPE changes by $mgh$ when you climb height $h$ .

Worked. A $60\,\text{kg}$ student climbs $3\,\text{m}$ of stairs.

$\Delta \text{GPE} = 60 \times 9.8 \times 3 = 1764\,\text{J}$ .

KE ↔ GPE swap (no friction). A pendulum, a roller coaster, a ball dropped — all move energy between KE and GPE conservatively if friction is ignored.

Without friction, GPE and KE swap back and forth; their total stays constant.

KE $= \dfrac{1}{2}mv^{2}$ .
$\Delta$ GPE $= mg\Delta h$ .
$v \to 2v$ : KE × 4.
Without friction: KE + GPE constant.

Work done and power

$W = Fd$ . $P = E/t$ . Both use joules.

Work done. $W = F \times d,$ where $F$ is the force ( $\text{N}$ ) and $d$ is the distance moved IN THE DIRECTION OF THE FORCE ( $\text{m}$ ). Units: joules.

$W =$ energy transferred. When you push a box and it moves, your work done = energy transferred from your muscles to the box's KE / heat / etc.

Power. $P = \dfrac{E}{t} = \dfrac{W}{t}.$

Power is the RATE of energy transfer. Units: watts ( $\text{W}$ ), where $1\,\text{W} = 1\,\text{J/s}$ .

Worked. A motor lifts $200\,\text{N}$ through $5\,\text{m}$ in $4\,\text{s}$ .

$W = Fd = 200 \times 5 = 1000\,\text{J}$ .
$P = 1000/4 = 250\,\text{W}$ .

Tip. Distance must be in the SAME DIRECTION as the force. If a force is sideways while the object moves forward, that force does NO work.

$W = Fd$ (force × distance in direction).
$P = E/t$ .
$1\,\text{W} = 1\,\text{J/s}$ .
Sideways forces do no work.

Efficiency

Useful output divided by total input, expressed as a percentage.

Efficiency formula. $\text{efficiency} = \dfrac{\text{useful energy output}}{\text{total energy input}} \times 100\%.$

Or equivalently for power: $\text{efficiency} = \dfrac{\text{useful power output}}{\text{total power input}} \times 100\%.$

Worked. A motor uses $400\,\text{J}$ of electrical energy to lift a load by $300\,\text{J}$ of GPE. Find efficiency.

$300/400 \times 100 = 75\%$ .
Wasted: $100\,\text{J}$ , mostly as heat in the motor.

Real systems. Always less than 100%. Efficiency lost mostly as heat (friction in moving parts) and sound.

Conservation isn't violated. $400\,\text{J}$ input → $300\,\text{J}$ useful + $100\,\text{J}$ wasted. Total still $400$ .

Efficiency = useful / total × 100%.
Always less than 100% in real systems.
Wasted energy mostly heat / sound.
Conservation not violated; energy just changes form.

Energy resources

Where useful energy and electrical power come from — and the trade-offs of each.

Obtaining useful energy. The 0625 syllabus lists the resources used to obtain useful energy or generate electrical power:

Fossil fuels (coal, oil, gas) — chemical energy released by burning. The heat boils water; the steam turns a turbine that drives a generator to produce electricity.
Biofuels — chemical energy in plant or animal matter (wood, ethanol, biogas). Burned the same way as fossil fuels, via boiler → turbine → generator.
Water — energy stored in waves, in tides, and in water behind a hydroelectric dam. Moving water turns a turbine connected to a generator.
Geothermal — heat from hot rocks deep inside the Earth. Water is pumped down, returns as steam, and drives a turbine and generator.
Nuclear fuel — energy released by nuclear fission. The heat boils water; steam drives a turbine and generator.
Solar cells — use light from the Sun to generate electrical power directly (no turbine).
Solar panels — use infrared and other electromagnetic waves from the Sun to heat water directly.
Wind — moving air (caused by the Sun heating the air unevenly) turns wind turbines connected to generators.

The boiler-turbine-generator chain. Fossil-fuel, biofuel, nuclear and geothermal stations all share the same chain: a heat source boils water → high-pressure steam spins a turbine → the turbine drives a generator → electricity. Only the heat source differs.

Energy from the Sun. Radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal. Fossil fuels and biofuels store energy that plants captured from sunlight; wind and waves come from the Sun heating the air and oceans; hydroelectric water was lifted by the Sun-driven water cycle.

The Sun's own energy comes from nuclear fusion — light hydrogen nuclei join to form helium, releasing energy. Research is being carried out into using nuclear fusion to generate electrical energy on a large scale on Earth.

Advantages and disadvantages — compare resources on renewability, availability, reliability, scale and environmental impact:

Resource	Renewable?	Reliable?	Environmental impact
Fossil fuels	No	Yes (on demand)	CO₂, pollution
Biofuels	Yes	Yes	CO₂ when burned, but crops re-absorb it
Hydroelectric	Yes	Yes	Floods land behind the dam
Waves / tides	Yes	Tides predictable; waves less so	Low; can affect habitats
Geothermal	Yes	Yes	Low; limited to suitable sites
Nuclear	No	Yes	Radioactive waste; risk of accident
Solar	Yes	No (no Sun at night)	Very low in use
Wind	Yes	No (depends on wind)	Very low in use; large land area

Fossil fuels, biofuels, nuclear and geothermal: heat → boiler → turbine → generator.
Solar cells generate electricity directly; solar panels heat water.
Sun is the main source for all resources except geothermal, nuclear and tidal.
The Sun's energy comes from nuclear fusion of hydrogen into helium.
Compare resources on renewability, availability, reliability, scale and environmental impact.

How it’s examined

Energy + work + power appears every Paper 4 (8-12 marks), often as a multi-part question chaining KE, GPE, work, power and efficiency. Examiner reports flag using force × total distance instead of distance in direction, and forgetting that efficiency is a percentage.

Sources: Cambridge IGCSE Physics 0625 syllabus 2026-2028 (1.7); 0625/42 Oct/Nov 2024 — Q9 (KE-GPE-efficiency chain); 0625 Examiner Reports 2022-2024. Last reviewed 2026-05-06.

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Step-by-step worked examples — Energy, Work and Power

Step-by-step solutions to past-paper-style questions on energy, work and power, written exactly the way a tutor would explain them at the board.

1Kinetic energy
Core• KE
Question
A $2\,\text{kg}$ ball moves at $6\,\text{m/s}$ . Find its kinetic energy.
Step-by-step solution
1. Step 1
  $E_{k} = \dfrac{1}{2} mv^{2}$ .
  $E_{k} = \dfrac{1}{2}(2)(6^{2}) = 36\,\text{J}$
Answer
$36\,\text{J}$
2Gravitational potential energy
Core• GPE
Question
Lift a $5\,\text{kg}$ box $3\,\text{m}$ vertically. Find the GPE gained. Take $g = 10\,\text{N/kg}$ .
Step-by-step solution
1. Step 1
  $\Delta E_{p} = mgh$ .
  $\Delta E_{p} = 5 \times 10 \times 3 = 150\,\text{J}$
Answer
$150\,\text{J}$
3Work done by a force
Extended• Adapted from 0625/42 May/Jun 2024 Q7• work
Question
A horizontal force of $25\,\text{N}$ pushes a box $4\,\text{m}$ along the floor. Find the work done.
Step-by-step solution
1. Step 1
  $W = Fd$ .
  $W = 25 \times 4 = 100\,\text{J}$
Answer
$100\,\text{J}$
4Power
Extended• power
Question
A motor lifts a $200\,\text{N}$ load through $5\,\text{m}$ in $4\,\text{s}$ . Find the average power.
Step-by-step solution
1. Step 1
  Work done.
  $W = 200 \times 5 = 1000\,\text{J}$
2. Step 2
  Power.
  $P = \dfrac{W}{t} = \dfrac{1000}{4} = 250\,\text{W}$
Answer
$250\,\text{W}$
5Conservation of energy
Extended• conservation
Question
A ball of mass $0.5\,\text{kg}$ is dropped from $20\,\text{m}$ . Ignore air resistance, $g = 10\,\text{m/s}^{2}$ . Find its speed just before hitting the ground using energy.
Step-by-step solution
1. Step 1
  GPE lost = KE gained.
  $mgh = \dfrac{1}{2} m v^{2}$
2. Step 2
  Cancel $m$ , solve.
  $v = \sqrt{2gh} = \sqrt{2 \times 10 \times 20} = 20\,\text{m/s}$
Answer
$20\,\text{m/s}$
6Work done against friction
Core• work, friction
Question
A box is dragged $15\,\text{m}$ across a floor against a constant frictional force of $40\,\text{N}$ . Find the work done against friction.
Step-by-step solution
1. Step 1
  $W = F d$ with force along motion.
  $W = 40 \times 15 = 600\,\text{J}$
Answer
$600\,\text{J}$
7GPE on a ramp — height NOT slope length
Extended• GPE, incline
Question
A $2.0\,\text{kg}$ box is pushed $5.0\,\text{m}$ up a frictionless ramp inclined at $30^{\circ}$ . Take $g = 10\,\text{N/kg}$ . Find the gain in GPE.
Step-by-step solution
1. Step 1
  Vertical height from $h = L\sin\theta$ .
  $h = 5.0 \times \sin 30^{\circ} = 5.0 \times 0.5 = 2.5\,\text{m}$
2. Step 2
  $\Delta E_{p} = mgh$ .
  $\Delta E_{p} = 2.0 \times 10 \times 2.5 = 50\,\text{J}$
Answer
$50\,\text{J}$
Examiner tip
The examiner report flags candidates often substitute the $5\,\text{m}$ slope length directly into $mgh$ — but $h$ is the VERTICAL rise.
8Beyond 0625 — energy stored in a stretched spring
Challenge• spring, elastic PE, beyond-0625
Question
A spring with spring constant $k = 150\,\text{N/m}$ is stretched by $0.20\,\text{m}$ . Find the elastic potential energy stored.
Step-by-step solution
1. Step 1
  $E = \tfrac{1}{2} k x^{2}$ .
  $E = \tfrac{1}{2} \times 150 \times (0.20)^{2}$
2. Step 2
  Evaluate.
  $E = \tfrac{1}{2} \times 150 \times 0.04 = 3.0\,\text{J}$
Answer
$3.0\,\text{J}$
Examiner tip
Enrichment beyond the Cambridge IGCSE 0625 syllabus. The elastic potential energy formula $E = \tfrac{1}{2}kx^{2}$ is not required on 0625 — §1.7.1 lists elastic (strain) energy only as an energy store, and there is no formula for it on the 0625 data sheet. The formula belongs to A-level (and other-board IGCSE) physics. On 0625, the energy stored equals the work done stretching the spring (area under the load-extension graph).
9Efficiency of a motor
Extended• efficiency
Question
An electric motor uses $400\,\text{J}$ of electrical energy to lift a $20\,\text{N}$ weight by $12\,\text{m}$ . Find the efficiency.
Step-by-step solution
1. Step 1
  Useful output = GPE gained = $Fh$ .
  $E_{\text{out}} = 20 \times 12 = 240\,\text{J}$
2. Step 2
  Efficiency.
  $\eta = \dfrac{240}{400} \times 100\% = 60\%$
Answer
$60\%$
10Power from $P = Fv$
Extended• power, P=Fv
Question
A car travels at a steady $25\,\text{m/s}$ . Total resistive force (air + friction) is $600\,\text{N}$ . Find the output power needed from the engine.
Step-by-step solution
1. Step 1
  At constant velocity, engine driving force = resistive force.
  $F = 600\,\text{N}$
2. Step 2
  Power $P = Fv$ (derive: $P = W/t = Fd/t = Fv$ ).
  $P = 600 \times 25 = 15{,}000\,\text{W} = 15\,\text{kW}$
Answer
$15\,\text{kW}$
Examiner tip
The examiner report flags candidates often try $P = E/t$ without realising they have no time — recognise that $P = Fv$ shortcuts directly when speed is constant.
11Show that doubling speed quadruples kinetic energy
Extended• KE, ratio
Question
A $1200\,\text{kg}$ car has its speed increased from $15\,\text{m/s}$ to $30\,\text{m/s}$ . Show that the kinetic energy quadruples, and find the increase.
Step-by-step solution
1. Step 1
  Initial KE.
  $E_{k,1} = \tfrac{1}{2}(1200)(15)^{2} = 135{,}000\,\text{J}$
2. Step 2
  Final KE.
  $E_{k,2} = \tfrac{1}{2}(1200)(30)^{2} = 540{,}000\,\text{J}$
3. Step 3
  Ratio = $540{,}000 / 135{,}000 = 4$ . KE is proportional to $v^{2}$ so doubling $v$ multiplies KE by $2^{2} = 4$ .
4. Step 4
  Increase.
  $\Delta E_{k} = 540{,}000 - 135{,}000 = 405{,}000\,\text{J}$
Answer
$E_{k}$ quadruples; increase $= 4.05 \times 10^{5}\,\text{J}$ .
Examiner tip
The 2024 mark scheme awards a 'show that' mark only if both KE values are calculated and the ratio is stated — quoting $v^{2}$ alone is insufficient.
12Classify energy resources and trace them back to the Sun
Core• energy resources, the Sun, classify
Question
A power company lists its energy resources: coal, wind, hydroelectric, geothermal, nuclear and solar cells. (a) State which TWO of these do NOT ultimately get their energy from the Sun. (b) Explain how wind power ultimately traces back to the Sun.
Step-by-step solution
1. Step 1
  Radiation from the Sun is the main source of energy for all our energy resources EXCEPT geothermal, nuclear and tidal.
2. Step 2
  From the company's list, the two resources not powered by the Sun are geothermal (heat from inside the Earth) and nuclear (energy stored in nuclei of nuclear fuel).
3. Step 3
  Wind chain: the Sun heats the Earth's surface unevenly. Warm air rises, cooler air moves in to replace it — these convection currents are wind. The moving air turns wind turbines, which drive a generator to produce electricity.
Answer
(a) Geothermal and nuclear. (b) Sun heats the air unevenly → convection currents (wind) → turbine → generator → electricity.
Examiner tip
Supplement statement 1.7.3.4: the only resources NOT from the Sun are geothermal, nuclear and tidal. Coal, wind, hydroelectric, waves, biofuels and solar all trace back to the Sun.
13Efficiency of a boiler-turbine-generator energy chain
Extended• energy resources, efficiency, power station
Question
A fossil-fuel power station burns coal that releases $2000\,\text{MJ}$ of chemical energy each second. The boiler transfers $1500\,\text{MJ}$ of this to the steam; the turbine and generator together deliver $700\,\text{MJ}$ of electrical energy each second. Find (a) the overall efficiency of the power station, and (b) the electrical power output.
Step-by-step solution
1. Step 1
  The chain is: chemical energy in fuel → boiler heats water to steam → steam turns the turbine → turbine drives the generator → electrical energy.
2. Step 2
  Overall efficiency compares useful electrical output to total chemical input.
  $\eta = \dfrac{700}{2000} \times 100\% = 35\%$
3. Step 3
  Electrical power output = energy transferred per second.
  $P = \dfrac{E}{t} = \dfrac{700 \times 10^{6}\,\text{J}}{1\,\text{s}} = 7.0 \times 10^{8}\,\text{W}$
Answer
(a) $35\%$ . (b) $7.0 \times 10^{8}\,\text{W} = 700\,\text{MW}$ .
Examiner tip
Most wasted energy leaves as heat — in the hot exhaust gases, the cooling water and friction in the turbine. The boiler-turbine-generator chain is examined for fossil fuels, biofuels, nuclear and geothermal stations.
14Compare a renewable and a non-renewable resource
Core• energy resources, advantages, disadvantages
Question
A remote island must choose between a diesel (fossil-fuel) generator and a wind farm to supply electricity. Give one advantage and one disadvantage of EACH, judged on renewability, reliability and environmental impact.
Step-by-step solution
1. Step 1
  Diesel generator — advantage: reliable, it can supply power on demand at any time, day or night, whatever the weather; it is also compact for the power produced.
2. Step 2
  Diesel generator — disadvantage: it burns a non-renewable fossil fuel that will run out, and it releases carbon dioxide (a greenhouse gas) and other pollutants.
3. Step 3
  Wind farm — advantage: wind is renewable and free, and generating electricity from it produces no carbon dioxide or fuel cost.
4. Step 4
  Wind farm — disadvantage: it is unreliable because output depends on the wind; it produces nothing when the wind is too weak or too strong, and turbines take up a large area.
Answer
Diesel: + reliable, on-demand power; − non-renewable and emits CO₂. Wind: + renewable and no CO₂ in use; − unreliable, depends on the wind.
Examiner tip
Supplement statement 1.7.3.2 asks for advantages and disadvantages in terms of renewability, availability, reliability, scale and environmental impact. Answers must compare on these named criteria, not give vague statements like 'wind is good'.
15The Sun's energy source — nuclear fusion
Core• the Sun, nuclear fusion
Question
(a) State the process by which energy is released in the Sun. (b) Solar panels on a roof receive $350\,\text{W}$ of infrared and other radiation per square metre. A panel of area $4.0\,\text{m}^{2}$ heats water with an efficiency of $60\%$ . Find the useful power transferred to the water.
Step-by-step solution
1. Step 1
  (a) Energy is released in the Sun by nuclear fusion — light nuclei (hydrogen) join to form heavier nuclei (helium), releasing energy.
2. Step 2
  (b) Total radiation power reaching the panel = intensity × area.
  $P_{\text{in}} = 350 \times 4.0 = 1400\,\text{W}$
3. Step 3
  Useful power = efficiency × input power.
  $P_{\text{useful}} = 0.60 \times 1400 = 840\,\text{W}$
Answer
(a) Nuclear fusion of hydrogen into helium. (b) $840\,\text{W}$ .
Examiner tip
Supplement statements 1.7.3.5-6: energy is released by nuclear fusion in the Sun, and research is being carried out into using fusion to generate electricity on a large scale. Note a solar panel HEATS water, while a solar cell generates electricity directly.
16A* — pumped-storage hydroelectric synoptic
Challenge• synoptic, power
Question
A pumped-storage scheme releases $5.0 \times 10^{6}\,\text{kg}$ of water from a reservoir $80\,\text{m}$ above the turbines, over $20$ minutes. Generation efficiency is $75\%$ . Take $g = 10\,\text{m/s}^{2}$ . Find the average electrical power output.
Step-by-step solution
1. Step 1
  Total GPE released.
  $\Delta E_{p} = mgh = 5.0 \times 10^{6} \times 10 \times 80 = 4.0 \times 10^{9}\,\text{J}$
2. Step 2
  Useful electrical energy (75% efficient).
  $E_{\text{elec}} = 0.75 \times 4.0 \times 10^{9} = 3.0 \times 10^{9}\,\text{J}$
3. Step 3
  Convert time.
  $t = 20 \times 60 = 1200\,\text{s}$
4. Step 4
  Average power.
  $P = \dfrac{E_{\text{elec}}}{t} = \dfrac{3.0 \times 10^{9}}{1200} = 2.5 \times 10^{6}\,\text{W}$
Answer
$2.5 \times 10^{6}\,\text{W} = 2.5\,\text{MW}$
Examiner tip
The 2024 mark scheme awards method marks for applying efficiency to the energy (not the height or the power) and for converting minutes to seconds before dividing.

Key Formulae — Energy, Work and Power

The formulae you need to memorise for energy, work and power on the Cambridge IGCSE 0625 paper, with every variable defined in plain English and a note on when to use it.

Kinetic energy
$E_{k} = \dfrac{1}{2} m v^{2}$
$m$
mass in kg
$v$
speed in m/s
When to use
Any object with mass and motion.
Change in GPE
$\Delta E_{p} = mgh$
$h$
vertical height (NOT distance travelled)
When to use
Object raised or lowered in a uniform gravity field.
Work done
$W = Fd$
$F$
force in direction of motion
$d$
distance moved IN that direction
When to use
Constant force acting on a moving object.
Power
$P = \dfrac{W}{t} = \dfrac{E}{t}$
$P$
power in watts (W)
When to use
Rate of doing work or transferring energy.
Efficiency
$\text{efficiency} = \dfrac{\text{useful energy out}}{\text{total energy in}} \times 100\%$
When to use
Comparing useful output to input — answer is between 0% and 100%.

Key Definitions and Keywords — Energy, Work and Power

Definitions to memorise and the exact keywords mark schemes credit for energy, work and power answers — sharpened from recent examiner reports for the 2026 0625 sitting.

Energy
Examiner keyword
Capacity to do work. Scalar; SI unit joule (J).
Work
Examiner keyword
Energy transferred when a force moves its point of application along its line of action.
Power
Examiner keyword
Rate at which work is done or energy is transferred. Unit watt (W).
Principle of conservation of energy
Examiner keyword
Energy cannot be created or destroyed, only transferred from one store to another.
Efficiency
Examiner keyword
The fraction of input energy that becomes useful output. Always less than 100% for real machines.
Renewable energy resource
Examiner keyword
An energy resource that is replenished naturally and will not run out, e.g. wind, water (waves, tides, hydroelectric), geothermal and solar.
Non-renewable energy resource
Examiner keyword
An energy resource with a finite supply that will eventually run out, e.g. fossil fuels and nuclear fuel.
Nuclear fusion (in the Sun)
Examiner keyword
The joining of light nuclei (hydrogen) to form heavier nuclei (helium), releasing energy. It is the process that releases energy in the Sun.

Common Mistakes and Misconceptions — Energy, Work and Power

The traps other students keep falling into on energy, work and power questions — taken from recent Cambridge IGCSE 0625 examiner reports and mark schemes — and how to avoid them.

✕Using slope distance for $h$ in $mgh$
0625/42 — recurring
Why it happens
Substituting whatever distance the question quotes.
How to avoid it
$h$ is the VERTICAL height change. For a ramp, use $h = L \sin\theta$ .
✕Forgetting to square velocity in KE
Why it happens
Speed.
How to avoid it
$E_{k} = \dfrac{1}{2} m v^{2}$ — the $v$ is squared.
✕Quoting power in joules
Why it happens
Confusing energy with power.
How to avoid it
Power = energy / time, units watts (W) = J/s.
✕Getting an efficiency > 100%
Why it happens
Inverting numerator and denominator.
How to avoid it
Useful out goes ON TOP, total in goes UNDERNEATH. Always between 0 and 100%.
✕Confusing a solar cell with a solar panel
0625 — recurring
Why it happens
Both sit on roofs and both use sunlight.
How to avoid it
A solar cell uses light from the Sun to generate electricity directly. A solar panel uses infrared and other waves from the Sun to heat water.
✕Saying tidal power comes from the Sun
Why it happens
Assuming all water-based resources are solar.
How to avoid it
Tides are caused mainly by the Moon's gravity, so tidal is one of the three resources (with geothermal and nuclear) that do NOT come from the Sun. Waves and hydroelectric DO come from the Sun.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Video lesson

Short walkthrough of the concepts students most often get stuck on.

Energy, Work and Power — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Energy, Work and Power

Short Study Notes in the form of Slides

Detailed Notes

What you’ll learn

How it’s examined

1Kinetic energy

2Gravitational potential energy

3Work done by a force

4Power

5Conservation of energy

6Work done against friction

7GPE on a ramp — height NOT slope length

8Beyond 0625 — energy stored in a stretched spring

9Efficiency of a motor

10Power from P=FvP = FvP=Fv

11Show that doubling speed quadruples kinetic energy

12Classify energy resources and trace them back to the Sun

13Efficiency of a boiler-turbine-generator energy chain

14Compare a renewable and a non-renewable resource

15The Sun's energy source — nuclear fusion

16A* — pumped-storage hydroelectric synoptic

Kinetic energy

Change in GPE

Work done

Power

Efficiency

Energy

Work

Power

Principle of conservation of energy

Efficiency

Renewable energy resource

Non-renewable energy resource

Nuclear fusion (in the Sun)

✕Using slope distance for hhh in mghmghmgh

✕Forgetting to square velocity in KE

✕Quoting power in joules

✕Getting an efficiency > 100%

✕Confusing a solar cell with a solar panel

✕Saying tidal power comes from the Sun

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Energy, Work and Power — frequently asked questions

10Power from $P = Fv$

✕Using slope distance for $h$ in $mgh$