Energy stores and transfers Edexcel International GCSE Science (Double Award) revision
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In plain words
Energy isn't used up: it moves from one store to another. A ball at the top of a hill has energy in its gravitational store; as it rolls down, that moves into its kinetic (movement) store. Some always ends up warming the surroundings, which is the "wasted" part.
Three things to know
- Energy is stored (kinetic, gravitational potential, chemical, elastic, nuclear, thermal) and transferred (by forces, electric currents, heating and waves). It is never created or destroyed.
- Kinetic energy = ½ × mass × speed² (Ek = ½mv²).
- Change in gravitational potential energy = mass × g × change in height (ΔEp = mgΔh).
Worked example
Find the kinetic energy of a 2 kg ball moving at 3 m/s.
- Kinetic energy = ½ × m × v².
- = ½ × 2 × 3² = ½ × 2 × 9.
- = 9 J.
Tips and tricks
- Square the speed before you do anything else. Forgetting the ² is the most common slip.
- "Energy is lost" earns nothing. Say where it went: "transferred to the surroundings as thermal energy".
It lands in your notebook with its questions as flashcards.
Energy stores and transfers: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is the kinetic energy of a 2 kg object moving at 3 m/s?
½ × 2 × 3² = 9 J.
A 5 kg mass is raised 4 m. Taking g as 10 N/kg, how much gravitational potential energy does it gain?
mgh = 5 × 10 × 4.
The speed of a car doubles. What happens to its kinetic energy?
Kinetic energy depends on speed squared.
Which energy store does a stretched catapult have?
Energy is stored in anything stretched or squashed.
A ball falls from a height. Ignoring air resistance, what happens to its energy?
It loses height and gains speed, and the total stays the same.
What does the principle of conservation of energy say?
Energy is only ever transferred from one store to another.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 10 marks. Write your answers on paper, then check them.
Energy stores and transfers
Edexcel International GCSE Science (Double Award) 4SD0 · 10 marks · papermunch.org
Name ______________________________ Date ______________
Calculate the kinetic energy of a 1200 kg car travelling at 10 m/s.[2]
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60 000 J. ½ × 1200 × 10².
A 2.0 kg book is lifted 1.5 m onto a shelf. Calculate the gain in gravitational potential energy. Take g = 9.8 N/kg.[2]
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29 J (29.4 J). 2.0 × 9.8 × 1.5.
A 0.50 kg ball is dropped from a height of 5.0 m. Ignoring air resistance and taking g = 10 N/kg, calculate its speed just before it hits the ground.[4]
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10 m/s. Energy = 0.50 × 10 × 5.0 = 25 J; ½ × 0.50 × v² = 25, so v² = 100.
Describe the energy transfers when a battery-powered torch is switched on.[2]
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Chemical energy in the battery is transferred by the electric current to light, and to thermal energy in the surroundings.
Answers: Energy stores and transfers
- 1. 60 000 J. ½ × 1200 × 10².
- 2. 29 J (29.4 J). 2.0 × 9.8 × 1.5.
- 3. 10 m/s. Energy = 0.50 × 10 × 5.0 = 25 J; ½ × 0.50 × v² = 25, so v² = 100.
- 4. Chemical energy in the battery is transferred by the electric current to light, and to thermal energy in the surroundings.