Edexcel IAL Physics: Materials — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Materials revision notes and the full study guide.

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Questions

1. State Stokes’ law and the conditions under which it applies. [4]

2. A steel sphere falls at terminal velocity through oil.

(a) Name the three forces acting and state the equation relating them. [3] (b) Explain why a common error is to omit one of them. [2]

3. State and explain how viscosity varies with temperature in (a) a liquid, (b) a gas. [4]

4. A wire of length 1.80 m and diameter 0.36 mm extends by 2.4 mm under a load of 32 N.

(a) Calculate the cross-sectional area. [2] (b) Calculate the stress and strain. [3] (c) Calculate the Young modulus. [2] (d) Calculate the energy stored in the wire. [2]

5. Explain the difference between elastic and plastic behaviour, and name the point on a stress–strain graph that separates them. [3]

6. Rubber shows hysteresis.

(a) Explain what this means. [2] (b) State what the area between the loading and unloading curves represents. [1] (c) Explain why a rubber ball does not bounce back to its original height. [2]

7. Define the terms strong, stiff, tough, brittle and ductile. [5]

8. Glass has a higher Young modulus than copper but shatters with almost no warning under a large enough load, while copper deforms visibly and absorbs a great deal of energy before it eventually breaks. Using the terms from Q7, describe glass and describe copper. [4]

9. On a force-extension graph, distinguish between the limit of proportionality and the elastic limit, and explain what happens at a yield point. [3]

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Answers

1. F = 6πηrv, where η is the fluid’s viscosity, r the sphere’s radius and v its speed [1]. It applies only for a small, spherical object [1], moving at low speed [1], with laminar (non-turbulent) flow [1].

2. (a) Weight downwards, upthrust upwards, viscous drag upwards [1] [1]. At terminal velocity: weight = upthrust + viscous drag [1]. (b) Upthrust is often omitted [1], because students treat the problem like free fall in air, where upthrust is negligible — in a dense liquid it is not [1].

3. (a) In a liquid, viscosity decreases as temperature rises [1], because the intermolecular forces are weakened, so layers slide past each other more easily [1]. (b) In a gas, viscosity increases with temperature [1], because faster molecular motion increases the transfer of momentum between layers [1].

4. (a) r = 0.18 mm = 1.8 × 10⁻⁴ m [1] A = πr² = 1.018 × 10⁻⁷ m² [1]. (b) stress = 32 ÷ 1.018 × 10⁻⁷ = 3.14 × 10⁸ Pa [1] [1] strain = 2.4 × 10⁻³ ÷ 1.80 = 1.33 × 10⁻³ [1]. (c) E = 3.14 × 10⁸ ÷ 1.33 × 10⁻³ [1] = 2.36 × 10¹¹ Pa [1]. (d) E = ½Fx = 0.5 × 32 × 2.4 × 10⁻³ [1] = 0.0384 J [1].

5. Elastic — the material returns to its original shape when the load is removed [1]. Plastic — a permanent deformation remains once the load is removed [1]. The point separating them is the elastic limit [1].

6. (a) The loading and unloading curves follow different paths [1], so the material does not return along the same route [1]. (b) The energy dissipated during the cycle, mostly as thermal energy [1]. (c) Some of the elastic potential energy is dissipated as heat during the deformation cycle [1], so less kinetic energy is available on the rebound and it cannot reach its original height [1].

7. Strong — high breaking stress [1]. Stiff — high Young modulus [1]. Tough — absorbs a large amount of energy before fracturing [1]. Brittle — breaks at the elastic limit with no plastic deformation [1]. Ductile — undergoes large plastic deformation and can be drawn into a wire [1].

8. Glass is strong (high breaking stress) and stiff (high Young modulus), but brittle and not tough — it breaks suddenly at its elastic limit, absorbing very little energy first [1] [1]. Copper is ductile (deforms plastically over a large range) and tough (absorbs a great deal of energy before breaking), but less stiff than glass, since its Young modulus is lower [1] [1].

9. The limit of proportionality is where the graph stops being a straight line through the origin [1]; the elastic limit is where the material stops returning to its original shape when the load is removed, and can occur slightly beyond the limit of proportionality [1]. At a yield point, the material extends significantly with little or no further increase in force [1].

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Where marks are usually lost

• Omitting upthrust from the terminal velocity force balance.
• Assuming viscosity behaves the same way with temperature in liquids and gases.
• Using the diameter instead of the radius for area.
• Applying Stokes’ law to turbulent flow.
• Confusing strong, stiff and tough — they are five separate properties, and a material can be strong without being tough (glass) or tough without being especially stiff (copper).
• Treating the Young modulus as a property that depends on the object’s dimensions — it is a property of the material, independent of the sample’s length or cross-sectional area.