Grade 10 physics – Mechanical Properties of Materials Quiz
1. What is the quantity that measures how much a material stretches when a tensile force is applied, defined as extension divided by original length?
Strain is the ratio of extension (change in length) to the original length and is dimensionless. Stress is force per unit area, Young's modulus relates stress to strain, and tensile strength is the maximum stress a material can withstand.
2. Which law describes the linear relationship between stress and strain for small deformations in an elastic material?
Hooke's law states that within the elastic limit, stress is proportional to strain (σ = Eε). Newton's second law concerns force and acceleration, Archimedes is about buoyancy, and Pascal's law concerns pressure in fluids.
3. Which mechanical property is best described as a material's ability to absorb energy and plastically deform without fracturing?
Toughness measures the energy a material can absorb before breaking (area under stress-strain curve). Brittle materials break with little plastic deformation, malleability refers to forming under compressive stress, and hardness measures resistance to surface indentation.
4. What is the name of the point on a stress-strain graph beyond which permanent (plastic) deformation begins?
The elastic limit or yield point marks the end of elastic behaviour; beyond it deformation is permanent. The proportional limit is where linearity ends, ultimate tensile is maximum stress, and fracture is where the material breaks.
5. If a steel wire has a Young's modulus of about 200 GPa, what does a higher Young's modulus indicate about a material compared to another with lower modulus?
Young's modulus is a measure of stiffness: higher E means less strain for a given stress (stiffer). It does not directly indicate brittleness or density.
6. During a tensile test, the maximum stress a material withstands before necking and eventual fracture is called what?
Ultimate tensile strength (UTS) is the maximum engineering stress on the stress-strain curve before necking. Yield strength is where plastic deformation begins, elastic limit is similar to yield, and shear modulus relates shear stress to shear strain.
7. Which material behaviour is typical of glass at room temperature when loaded in tension?
Glass is brittle: it fractures with very little plastic deformation. Ductile materials (like mild steel) show significant plastic deformation; rubber is highly elastic; viscoelastic behaviour is typical of some polymers.
8. Which test commonly produces a stress–strain curve used to find Young's modulus, yield point and tensile strength?
A tensile test stretches a specimen while measuring load and extension, producing a stress–strain curve from which Young's modulus, yield point and tensile strength can be obtained. Hardness and impact tests give different information.
9. Which property describes resistance of a material to localised plastic deformation such as scratching or indentation?
Hardness measures resistance to surface indentation or scratching. Toughness is energy absorption before fracture, elasticity is reversible deformation, and ductility is the ability to undergo plastic deformation (e.g., to be drawn into wire).
10. Two springs are joined in series. How does the effective spring constant compare to the individual spring constants k1 and k2?
For springs in series, reciprocals add: 1/keff = 1/k1 + 1/k2, so keff = (k1*k2)/(k1 + k2). For parallel springs keff = k1 + k2.
11. A metal rod is loaded within its elastic limit and then unloaded. Which statement is true about its length after unloading?
Within the elastic limit, deformation is reversible: removing the load lets the rod return to its original length. Permanent change occurs only if the elastic limit is exceeded.
12. Which factor does NOT directly affect Young's modulus of a material?
Young's modulus is a material property dependent on bonding, structure, temperature and defects. It is independent of the applied force magnitude as long as the material remains in the elastic region.
13. What is ductility commonly measured by in a tensile test?
Ductility is measured by how much a material can plastically deform before fracture — often expressed as percent elongation or reduction in cross-sectional area at fracture.
14. Which material would be most suitable where a structure must flex repeatedly without breaking (high fatigue resistance)?
Ductile steels typically resist fatigue and can absorb cyclic stresses without sudden fracture. Brittle ceramics, glass, and cast iron are prone to crack growth and failure under repeated loading.
15. What happens to the cross-sectional area of a ductile metal specimen when it is stretched past the yield point and eventually necks?
After yielding and as plastic deformation continues, a ductile specimen develops a local reduction in cross-sectional area called necking, which leads to eventual fracture.
16. Which of the following is an example of shear stress?
Shear stress acts parallel to the area causing layers to slide past each other (scissors action). Stretching is tensile stress, compressing is compressive stress, and heating is thermal.
17. A beam in a classroom is required to resist bending without large deflection. Which property of the material is most directly relevant?
Young's modulus determines stiffness and how much a beam will deflect under load. Electrical conductivity, chemical reactivity and colour are unrelated to bending stiffness.
18. Why do engineers design safety factors when using materials for bridges and buildings?
Safety factors give margin against unknowns such as higher loads, imperfections, or environmental effects, ensuring structures remain safe. They are not intended to make structures heavier for its own sake.
19. Which of the following materials is generally considered ductile and can be drawn into wires?
Copper is ductile and easily drawn into wires. Glass, granite and brittle ceramics fracture easily and are not suitable for wire drawing.
20. What does the area under the stress–strain curve up to fracture represent?
The area under the entire stress–strain curve up to fracture equals the energy per unit volume a material can absorb before breaking — its toughness. Modulus is the initial slope, yield strength is a point on the curve, density is unrelated.
21. Which process will increase the hardness and decrease the ductility of a metal like steel?
Cold working introduces dislocations that increase hardness and reduce ductility. Annealing softens and restores ductility. Melting/recasting can change properties depending on processing; polishing affects surface finish only.
22. Which of the following best describes a brittle fracture compared to a ductile fracture?
Brittle fractures usually occur suddenly with little plastic deformation and often produce a flat, crystalline fracture surface. Ductile fractures show significant plastic deformation and necking before failure.
23. If a wire carries a weight causing a force of 100 N and the cross-sectional area is 2 x 10^-6 m^2, what is the tensile stress in the wire?
Stress = force/area = 100 N / (2×10^-6 m^2) = 50,000,000 Pa = 5×10^7 Pa.
24. Which outcome is expected when the temperature of a metal is increased, holding stress constant, near but below its melting point?
Increasing temperature usually makes metals more ductile and reduces stiffness (Young's modulus decreases). Brittleness and density typically do not increase with temperature.
25. What is the most appropriate description of shear modulus (G)?
Shear modulus G relates shear stress to shear strain (τ = G·γ). The ratio of tensile stress to tensile strain is Young's modulus; area under curve is toughness; maximum load before fracture relates to tensile strength.
26. In the context of mechanical properties, what is 'elastic energy' stored in a stretched spring equal to?
For a linear spring, the elastic potential energy stored is the work done to stretch it: (1/2) k x^2. kx is the force, not the energy; energy is not zero.