Calculate the change in GPE when a 5\,kg mass is raised 3\,m (g = 10\,N/kg). [2 marks]

Calculate the kinetic energy of a 2\,kg object moving at 6\,m/s. [2 marks]

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How do you calculate gravitational potential energy and kinetic energy, and how do they interchange?

Gravitational and kinetic energy: the change in gravitational potential energy equation, the kinetic energy equation, and how energy transfers between the two stores.

A focused answer to Edexcel GCSE Physics 3.1 and 3.2, covering the change in gravitational potential energy equation, the kinetic energy equation, the units and what each symbol means, and how energy transfers between the gravitational and kinetic stores, with worked calculations.

Generated by Claude Opus 4.89 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking
Gravitational potential energy
Kinetic energy
Transferring between the stores
How Edexcel examines this
Try this

What this dot point is asking

Edexcel statements 3.1 and 3.2 want you to recall and use the equation for the change in gravitational potential energy when an object is raised, and the equation for the kinetic energy of a moving object, and to understand how energy transfers between these two stores.

Gravitational potential energy

The height that matters is the vertical height gained or lost, not the distance moved along a slope. If an object is pushed up a ramp, only the vertical rise counts towards the change in GPE. On Earth you use $g \approx 10\,\text{N/kg}$ , the same value as the gravitational field strength used for weight.

Kinetic energy

The most important feature of this equation is that the speed is squared, so kinetic energy grows much faster than speed: doubling the speed gives four times the kinetic energy. This is the physics behind the steep rise in braking distance with speed, because all of that kinetic energy must be removed by the braking force.

Transferring between the stores

A falling ball, a swinging pendulum and a roller-coaster all show this interchange. Ignoring resistive forces, the energy simply moves from one store to the other and the total stays the same, which is the idea of conservation of energy. Setting $\Delta GPE = KE$ lets you find a falling object's speed or the height a launched object reaches.

Worked example: speed of a falling object

A $2\,\text{kg}$ ball is dropped from rest and falls $5\,\text{m}$ . Ignoring air resistance, calculate its speed just before it hits the ground ( $g = 10\,\text{N/kg}$ ).

Step 1: Set the GPE lost equal to the KE gained

Because there is no air resistance, energy is conserved: all the gravitational potential energy lost by the falling ball is transferred to kinetic energy. We can write the energy stores as equal.

mg\Delta h = \tfrac{1}{2}mv^2

Step 2: Cancel the mass and rearrange for $v^2$

The mass $m$ appears on both sides, so it cancels. This is useful because it means the speed of a falling object (ignoring air resistance) does not depend on its mass.

g\Delta h = \tfrac{1}{2}v^2 \implies v^2 = 2g\Delta h = 2 \times 10 \times 5 = 100

Step 3: Take the square root to find the speed

We have $v^2 = 100$ , so take the square root. Stopping at $v^2$ is a very common error.

v = \sqrt{100} = 10\,\text{m/s}

Final answer: The ball hits the ground at $10\,\text{m/s}$ .

How Edexcel examines this

These two equations are examined on both tiers and underpin much of Topics 3 and 8, so they recur in larger energy and forces questions as well as standalone calculations. The mark scheme typically gives a mark for the correct equation, a mark for substitution and a mark for the answer with its unit, so always write the equation first. Kinetic energy questions are designed to catch the unsquared speed, so make squaring the speed a deliberate first step. Gravitational potential energy questions often test whether you use the vertical height when an object moves up a slope or stairs, so read the geometry carefully. Higher-tier questions frequently combine the two by asking you to equate the GPE lost to the KE gained (or the reverse) to find a speed or a height, assuming no energy is dissipated; these reward setting $mg\Delta h = \frac{1}{2}mv^2$ , cancelling the mass, and solving. Keep every quantity in SI units, because a height in centimetres or a mass in grams is a frequent source of lost marks.

Try this

Q1. Calculate the change in GPE when a $5\,\text{kg}$ mass is raised $3\,\text{m}$ ( $g = 10\,\text{N/kg}$ ). [2 marks]

Cue. $\Delta GPE = mg\Delta h = 5 \times 10 \times 3 = 150\,\text{J}$ .

Q2. Calculate the kinetic energy of a $2\,\text{kg}$ object moving at $6\,\text{m/s}$ . [2 marks]

Cue. $KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 2 \times 6^2 = 36\,\text{J}$ .

Exam-style practice questions

Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Edexcel 20193 marksA book of mass

0.8\,\text{kg}

is lifted from the floor onto a shelf

2.5\,\text{m}

above. The gravitational field strength is

10\,\text{N/kg}

. Calculate the change in gravitational potential energy of the book.

Show worked answer →

Use $\Delta GPE = m \times g \times \Delta h$ with $m = 0.8\,\text{kg}$ , $g = 10\,\text{N/kg}$ and $\Delta h = 2.5\,\text{m}$ (1 mark). Substitute: $\Delta GPE = 0.8 \times 10 \times 2.5 = 20\,\text{J}$ (2 marks for substitution and answer with the unit joules). Markers reward selecting the equation, correct substitution and the unit. A common error is to use the shelf height incorrectly or to drop the field strength.

Edexcel 20213 marksA car of mass

1200\,\text{kg}

travels at

20\,\text{m/s}

. Calculate the kinetic energy of the car. Use the equation

KE = \frac{1}{2} \times m \times v^2

Show worked answer →

Substitute $m = 1200\,\text{kg}$ and $v = 20\,\text{m/s}$ into $KE = \frac{1}{2}mv^2$ : $KE = \frac{1}{2} \times 1200 \times 20^2 = \frac{1}{2} \times 1200 \times 400$ (1 mark for squaring the speed), giving $KE = 240\,000\,\text{J}$ (2 marks). Markers reward squaring the speed before multiplying and the correct final value in joules. The classic error is to forget to square the speed, or to square the whole expression.

Related dot points

Sources & how we know this

Pearson Edexcel GCSE (9-1) Physics (1PH0) specification — Pearson (2016)
Edexcel GCSE Physics and Combined Science equation list (1PH0/1SC0) — Pearson (2025)