AQA GCSE Physics
AQA GCSE Physics 4.5.3 Forces and Elasticity Exam Questions
Free AQA GCSE Physics exam questions for 4.5.3 Forces and Elasticity, with a mark scheme for every pack. Covers elastic and inelastic deformation, Hooke's law F = ke, limit of proportionality, elastic potential energy and the spring practical.
4.5.3 Forces and Elasticity exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Physics 4.5.3 Forces and Elasticity
This AQA GCSE Physics section explains what happens when forces stretch, bend or compress an object. You need to distinguish elastic from inelastic deformation, use F = k e, calculate the energy stored in a stretched spring, and carry out the required practical on the relationship between force and extension. It is examined on Paper 2 and links back to elastic potential energy in 4.1.1.2. Examiners test reading force-extension graphs, identifying the limit of proportionality and finding the spring constant from a gradient.
What you need to know
- Changing shape To stretch, bend or compress an object, more than one force has to be applied. If only one force acts, the object would move rather than deform.
- Elastic and inelastic deformation An object that returns to its original length and shape after the forces are removed has been elastically deformed. One that does not has been inelastically deformed.
- Hooke's law The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. F = k e, where F is force in N, k is the spring constant in N/m and e is extension in m.
- Compression The same relationship applies to compression, where e is the compression of the object.
- Elastic potential energy A force that stretches or compresses a spring does work, and elastic potential energy is stored. Provided the limit of proportionality is not exceeded, work done equals elastic potential energy stored: Ee = 1/2 k e^2 (on the equation sheet).
- Force-extension graphs The graph is a straight line through the origin up to the limit of proportionality, then curves. The gradient of the linear part of a force (y) against extension (x) graph is the spring constant.
- Required practical Hang masses on a spring next to a ruler, record the extension (new length minus original length) for each force, read at eye level, and plot force against extension.
Common mistakes in 4.5.3 Forces and Elasticity
- Using the total length instead of the extension. Extension = stretched length minus original length.
- Saying Hooke's law always applies. It only applies up to the limit of proportionality.
- Confusing the elastic limit with the limit of proportionality. The AQA spec uses limit of proportionality for the end of the straight line.
- Using mass instead of weight. Convert hanging masses to force in newtons using W = m g.
- Leaving extension in cm with k in N/m. Convert to metres.
Try three 4.5.3 Forces and Elasticity exam-style questions
1. A spring has a spring constant of 25 N/m. Calculate the force needed to stretch it by 8.0 cm. (3 marks)
Show the mark scheme answer
e = 0.080 m; F = k e = 25 x 0.080; = 2.0 N.
2. Describe the difference between elastic and inelastic deformation. (2 marks)
Show the mark scheme answer
Elastic: the object returns to its original shape and length when the forces are removed; inelastic: the object does not return to its original shape (permanently deformed).
3. In the spring practical, a student measured the length of the spring rather than the extension. Explain why the force-length graph does not pass through the origin, and how to correct the results. (2 marks)
Show the mark scheme answer
At zero force the spring already has its original (unstretched) length, so the graph has an intercept; subtract the original length from each length to get the extension.
4.5.3 Forces and Elasticity FAQs
What does AQA GCSE Physics 4.5.3 Forces and elasticity cover?
It covers elastic and inelastic deformation, F = k e, the limit of proportionality, elastic potential energy and the force and extension required practical.
Which equations do I need?
Learn F = k e. The equation for elastic potential energy, Ee = 1/2 k e^2, is given on the equation sheet.
How do I find the spring constant from a graph?
Calculate the gradient of the straight-line part of a force against extension graph, using extension in metres, to get k in N/m.
