WJEC GCSE Physics
WJEC GCSE Physics 2.3 Work and Energy Exam Questions
Free WJEC GCSE Physics revision for 2.3 Work and Energy: what you need to know, common mistakes and exam-style questions with answers. Covers work done, kinetic energy, gravitational potential energy, elastic energy, Hooke's law, force-extension graphs, vehicle efficiency and car safety features.
Practise 2.3 Work and Energy with past papers
Once you have learnt this topic, find the 2.3 Work and Energy questions in real WJEC GCSE Physics past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About WJEC GCSE Physics 2.3 Work and Energy
Work and energy in Unit 2 links forces to energy transfer. You need to use W = Fd and understand that work done is energy transferred, then calculate kinetic energy, change in gravitational potential energy and elastic energy. Springs are covered with F = kx and elastic energy from the area under a force-extension graph, and the force-extension investigation is the specified practical. The topic also looks at energy losses in vehicles and how safety features such as air bags and crumple zones reduce injury. Examiners often set energy transfer calculations, such as an object falling and gaining kinetic energy, and ask for explanations of crumple zones.
What you need to know
- Work done Work done = force x distance moved in the direction of the force (W = Fd), in joules. Work done is equal to the energy transferred.
- Kinetic energy KE = 1/2 mv^2. Doubling speed makes the kinetic energy four times larger.
- Gravitational potential energy Change in potential energy = mgh, where h is the change in height. Ignoring air resistance, energy lost as PE when falling is gained as KE.
- Springs Force = spring constant x extension (F = kx) up to the limit of proportionality. Elastic energy stored = 1/2 Fx, the area under the force-extension graph. Investigating the force-extension graph for a spring is a specified practical.
- Vehicle efficiency Energy is wasted through air resistance (aerodynamic losses), rolling resistance, idling and braking (inertial losses). Streamlining and lighter vehicles improve fuel economy.
- Car safety Crumple zones and air bags increase the time and distance over which a vehicle or person stops, so the force on the occupants is smaller for the same energy and momentum change.
Common mistakes in 2.3 Work and Energy
- Forgetting to square the speed in KE = 1/2 mv^2. Square the velocity before multiplying by half the mass.
- Using the length of the spring instead of its extension. Extension = stretched length - original length.
- Saying crumple zones absorb the force. They absorb energy and increase the stopping time and distance, which reduces the force.
- Using the distance travelled at an angle in W = Fd. Use the distance moved in the direction of the force.
Try three 2.3 Work and Energy exam-style questions
1. Calculate the kinetic energy of a 1200 kg car travelling at 15 m/s. (2 marks)
Show the mark scheme answer
KE = 0.5 x 1200 x 15^2 = 0.5 x 1200 x 225; = 135 000 J.
2. A spring extends by 0.08 m with a 4 N load. Calculate the spring constant and the elastic energy stored. (3 marks)
Show the mark scheme answer
k = F / x = 4 / 0.08 = 50 N/m; energy = 0.5 x F x x = 0.5 x 4 x 0.08; = 0.16 J.
3. Explain how an air bag reduces the injuries to a driver in a crash. (3 marks)
Show the mark scheme answer
Air bag increases the time / distance taken for the driver to stop; so deceleration is smaller; so force on the driver is smaller.
2.3 Work and Energy FAQs
What does WJEC GCSE Physics 2.3 Work and Energy cover?
It covers work done, kinetic energy, gravitational potential energy, elastic energy, F = kx, force-extension graphs, energy losses in vehicles and car safety features.
Which unit is Work and Energy examined in?
It is examined in Unit 2: Forces, Space and Radioactivity, a 1 hour 45 minute written paper worth 45% of the GCSE, sat at foundation or higher tier. The Unit 3 practical assessment draws on the same practical skills.
What energy equations do I need?
Learn W = Fd, KE = 1/2 mv^2, ΔPE = mgh, F = kx and elastic energy = 1/2 Fx. Many questions link two of them, such as PE lost equals KE gained.
