Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall and use the equation to calculate the amounts of energy associated…
Full specification wording
Topic 8 – Energy – forces doing work: 8.9 Recall and use the equation to calculate the amounts of energy associated with a moving object: kinetic energy (joule, J) = 1/2 × mass (kilogram, kg) × (speed)² ((metre/second)², (m/s)²)
This equation gives the energy in an object's kinetic store because it is moving.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 9 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
This equation gives the energy in an object's kinetic store because it is moving. Multiply half the mass in kilograms by the square of the speed in metres per second: KE = ½ × m × v². Squaring the speed means doubling speed quadruples the kinetic energy. A 4 kg trolley moving at 3 m/s has KE = ½ × 4 × 3² = ½ × 4 × 9 = 18 J. Square the speed before multiplying by the mass, and keep mass in kilograms and speed in metres per second so the answer is in joules. Convert grams to kilograms and km/h to m/s first, because the squared unit (m/s)² depends on the speed being in the correct unit.
What earns the marks
- Squares the speed in metres per second before multiplying by half the mass in kilograms.
- Multiplies half the mass by the squared speed and states the result in joules.
- Converts mass to kilograms and speed to metres per second before substituting into the equation.
- Recognises that doubling the speed increases the kinetic energy by a factor of four because the speed is squared.
Common mistakes and how to put them right
Multiplies by the speed rather than its square.
Put it right: Square the speed first.
Doubles the mass instead of halving it.
Put it right: Use half the mass in the equation.
Leaves the speed in km/h or the mass in grams.
Put it right: Convert to m/s and kg before calculating.
Assumes doubling the speed doubles the energy.
Put it right: Recognise that the squared term makes it four times larger.
Exam tips
- Square the speed as a separate step so the arithmetic is easy to check.
- Write the unit of the answer as J and confirm mass and speed are in kg and m/s.
- Use the factor-of-four relationship to sense-check answers when speed changes.
Try the lesson
The start of the Topic 8 – Energy – forces doing work: 8.9 Recall and use the equation to calculate the amounts of energy associated with a moving object: kinetic energy (joule, J) = 1/2 × mass (kilogram, kg) × (speed)² ((metre/second)², (m/s)²) lesson, made from checked teaching notes for this specification point.
Have a go first
A 2 kg ball is rolling at 3 m/s. What is its kinetic energy?
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Test your understanding of Topic 8 – Energy – forces doing work: 8.9 Recall and use the equation to calculate the amounts of energy associated with a moving object: kinetic energy (joule, J) = 1/2 × mass (kilogram, kg) × (speed)² ((metre/second)², (m/s)²)
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