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The kinetic energy formula is Ek = ½mv², where m is mass in kg, v is speed in m/s and kinetic energy is in joules (J). Free GCSE Physics notes and 15 FAQs.
Kinetic Energy Calculations is part of Energy changes in a system, and the ways energy is stored before and after such changes in GCSE AQA Higher Physics.
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The kinetic energy formula is Ek = ½mv², where m is mass in kg, v is speed in m/s and kinetic energy is in joules (J). Free GCSE Physics notes and 15 FAQs.
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Use this lesson to stay inside Energy changes in a system, and the ways energy is stored before and after such changes while connecting the detail back to the wider Energy topic.
Read the core explanations from Kinetic Energy Calculations before testing yourself from memory.
A cricket ball flying towards you can break a window. A stationary cricket ball cannot. The difference? The moving ball has kinetic energy — energy stored in its motion.
This energy depends on two things: how heavy the object is (its mass) and how fast it's moving (its speed). But here's the twist — speed matters much more than you'd expect.
Notice that speed is squared in the formula. This means doubling the speed doesn't just double the kinetic energy — it quadruples it. A car travelling at 60 mph has four times more kinetic energy than the same car at 30 mph.
Kinetic energy calculations follow a clear pattern. The key is getting the units right and remembering to square the speed. Let's work through a typical exam question.
Worked example: Calculating Kinetic Energy
A 1200 kg car travels at 25 m/s. Calculate its kinetic energy. [3 marks]
Answer: 375,000 J (or 3.75 × 10⁵ J)
The most common mistake? Forgetting to square the speed. Students often calculate ½ × 1200 × 25 = 15,000 J instead of the correct 375,000 J. That's 25 times smaller than the right answer.
Here's something that surprises many students: in the kinetic energy formula, speed has a much bigger effect than mass. This is because speed is squared, but mass isn't.
Consider two scenarios: doubling the mass versus doubling the speed. If you double the mass, kinetic energy doubles. But if you double the speed, kinetic energy increases by a factor of four (2² = 4).
Worked example: Comparing Mass vs Speed Effects
Compare the kinetic energy of: (a) 2 kg object at 10 m/s, (b) 4 kg object at 10 m/s, (c) 2 kg object at 20 m/s
Answer: (a) 100 J, (b) 200 J, (c) 400 J
Exam questions love to test whether you can handle different units. The kinetic energy formula requires mass in kg and speed in m/s. If the question gives you grams or km/h, you must convert first.
Worked example: Unit Conversion Example
A 500 g ball moves at 36 km/h. Calculate its kinetic energy.
Answer: 25 J
Kinetic energy questions typically carry 3-4 marks. The mark scheme rewards method, substitution, and the final answer with units. Here's how to maximise your marks.
Remember the examiner's favourite tricks: giving mass in grams instead of kg, or speed in km/h instead of m/s. Always check the units before you start calculating.
This lesson focuses on kinetic energy, the energy stored in moving objects. At GCSE you should also recognise two other important mechanical stores: gravitational potential energy, stored when an object is raised, and elastic potential energy, stored when something is stretched or compressed. In many exam questions, energy is transferred between these stores rather than being created or destroyed.
For example, a rollercoaster at the top of a hill has gravitational potential energy. As it speeds up downhill, that store decreases while kinetic energy increases. A stretched spring stores elastic potential energy, which can then transfer into kinetic energy when released. Linking these stores helps you explain real situations, not just calculate one formula in isolation.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The kinetic energy formula is Ek = ½mv², where m is mass in kg, v is speed in m/s and kinetic energy is in joules (J). Kinetic energy is the energy stored in moving objects.
Kinetic energy is the energy stored in moving objects, measured in joules (J). It depends on the mass of the object and its speed. A moving cricket ball has kinetic energy and can break a window, whereas a stationary cricket ball cannot.
To calculate kinetic energy, substitute mass and speed into Ek = ½mv², remembering to square the speed. A 1200 kg car at 25 m/s has Ek = ½ × 1200 × 625 = 375,000 J.
The kinetic energy equation needs mass in kg and speed in m/s, giving energy in joules (J). Convert grams by dividing by 1000 and km/h by dividing by 3.6, so a 500 g ball at 36 km/h is 0.5 kg at 10 m/s, giving 25 J.
If speed doubles, kinetic energy quadruples, because speed is squared in Ek = ½mv² (2² = 4). Doubling the mass only doubles the kinetic energy, so speed has a much bigger effect than mass.
Speed affects kinetic energy more than mass because speed is squared and mass is not. A 2 kg object at 10 m/s has 100 J, a 4 kg object at 10 m/s has 200 J, and a 2 kg object at 20 m/s has 400 J.
The equation linking kinetic energy, mass and speed is Ek = ½mv², where Ek is kinetic energy in joules, m is mass in kg and v is speed in metres per second. Speed is squared, so it has a bigger effect than mass.
Kinetic energy, mass and speed are linked by Ek = ½mv², meaning kinetic energy equals half times mass times speed squared. A 1200 kg car at 25 m/s has Ek = ½ × 1200 × 25² = 375,000 J.
Kinetic energy doubles when the mass doubles, because mass is not squared in Ek = ½mv². A 2 kg object at 10 m/s has 100 J, while a 4 kg object at 10 m/s has 200 J.
The most common mistake in kinetic energy calculations is forgetting to square the speed. For a 1200 kg car at 25 m/s, calculating ½ × 1200 × 25 gives 15,000 J instead of the correct 375,000 J, which is 25 times too small.
Kinetic energy needs mass in kg, so grams are divided by 1000 first, and speed in km/h is divided by 3.6 to give m/s. A 500 g ball at 36 km/h has m = 0.5 kg and v = 10 m/s, so Ek = ½ × 0.5 × 10² = 25 J.
The kinetic energy of a 1200 kg car travelling at 25 m/s is 375,000 J, or 3.75 × 10⁵ J. Using Ek = ½mv², 25² = 625, and ½ × 1200 × 625 = 375,000 J.
A rollercoaster going downhill transfers energy from its gravitational potential energy store to its kinetic energy store. At the top of a hill it has gravitational potential energy, and as it speeds up downhill that store decreases while kinetic energy increases.
The mechanical energy stores are kinetic energy, stored in moving objects, gravitational potential energy, stored when an object is raised, and elastic potential energy, stored when something is stretched or compressed. Energy is transferred between these stores rather than being created or destroyed.
Speed in km/h is converted to m/s by dividing by 3.6 before using Ek = ½mv². For example, 36 km/h ÷ 3.6 = 10 m/s. The kinetic energy formula requires mass in kg and speed in m/s.