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301. Why is steel preferred over aluminum in construction of bridges?
ⓐ. Steel has lower density than aluminum
ⓑ. Steel has higher Young’s modulus than aluminum
ⓒ. Steel has higher electrical conductivity
ⓓ. Steel is cheaper than aluminum
Correct Answer: Steel has higher Young’s modulus than aluminum
Explanation: Steel’s Young’s modulus ($\sim 2 \times 10^{11} \, Pa$) is much higher than aluminum’s ($\sim 7 \times 10^{10} \, Pa$), making steel stiffer and more suitable for load-bearing structures like bridges.
302. For making springs, which property of material is most important?
ⓐ. High bulk modulus
ⓑ. High shear modulus
ⓒ. Low Young’s modulus
ⓓ. Low Poisson’s ratio
Correct Answer: High shear modulus
Explanation: Springs work under torsional deformation. Materials with high shear modulus (like steel) are chosen to resist twisting and store elastic energy.
303. Why is glass not preferred for making beams in construction?
ⓐ. It has high tensile strength
ⓑ. It has low compressive strength
ⓒ. It is brittle and has very little plastic region
ⓓ. It is too light in weight
Correct Answer: It is brittle and has very little plastic region
Explanation: Glass fails suddenly without significant plastic deformation. Hence, it is unsafe in load-bearing construction.
304. Which modulus determines the ability of a material to resist shape changes when used in machinery components?
ⓐ. Bulk modulus
ⓑ. Young’s modulus
ⓒ. Shear modulus
ⓓ. Elastic limit
Correct Answer: Shear modulus
Explanation: Machinery parts under torsion or shear loads (like shafts and gears) require materials with high shear modulus for durability.
305. For submarine hull design, which modulus is most relevant?
ⓐ. Young’s modulus
ⓑ. Shear modulus
ⓒ. Bulk modulus
ⓓ. Poisson’s ratio
Correct Answer: Bulk modulus
Explanation: Submarines face immense external hydrostatic pressure. Bulk modulus measures resistance to volume change, hence crucial for underwater vessel design.
306. Why is copper used in making electrical wires despite being less stiff than steel?
ⓐ. Copper has high density
ⓑ. Copper has high ductility and good conductivity
ⓒ. Copper has high shear modulus
ⓓ. Copper has high bulk modulus
Correct Answer: Copper has high ductility and good conductivity
Explanation: Copper’s ductility allows it to be drawn into wires without fracture. Its excellent electrical conductivity makes it ideal for wiring.
307. Which modulus plays the most important role in designing pressure cookers?
ⓐ. Young’s modulus
ⓑ. Bulk modulus
ⓒ. Shear modulus
ⓓ. Poisson’s ratio
Correct Answer: Bulk modulus
Explanation: Pressure cookers must withstand high fluid pressures. A high bulk modulus ensures resistance to volume compression under pressure.
308. Which property makes rubber suitable for making shock absorbers?
ⓐ. Very high Young’s modulus
ⓑ. Very low shear modulus and very high elasticity
ⓒ. High bulk modulus
ⓓ. Low ductility
Correct Answer: Very low shear modulus and very high elasticity
Explanation: Rubber deforms easily under stress and can absorb shocks. It regains its original shape due to high elasticity, making it ideal for damping vibrations.
309. Which property makes steel cables suitable for lifting heavy loads in cranes?
ⓐ. High Young’s modulus and high tensile strength
ⓑ. Low bulk modulus
ⓒ. High electrical resistivity
ⓓ. Low density
Correct Answer: High Young’s modulus and high tensile strength
Explanation: Steel has high tensile strength to bear heavy loads without failure and high Young’s modulus to avoid large elongations.
310. Why are materials with high ductility chosen in earthquake-resistant building design?
ⓐ. They are harder than brittle materials
ⓑ. They deform plastically before failure, absorbing energy
ⓒ. They have low thermal conductivity
ⓓ. They have high bulk modulus
Correct Answer: They deform plastically before failure, absorbing energy
Explanation: Ductile materials (like steel) absorb seismic energy by plastic deformation, preventing sudden collapse and making buildings safer.
311. Why is steel used as reinforcement in concrete structures?
ⓐ. Steel has high density
ⓑ. Steel has high compressive strength
ⓒ. Steel has high tensile strength and matches concrete in thermal expansion
ⓓ. Steel has low Young’s modulus
Correct Answer: Steel has high tensile strength and matches concrete in thermal expansion
Explanation: Concrete is strong in compression but weak in tension. Steel provides tensile strength and has similar thermal expansion, preventing cracks in reinforced concrete structures.
312. Which property of steel makes it ideal for building bridges and skyscrapers?
ⓐ. Low density
ⓑ. High Young’s modulus
ⓒ. Low bulk modulus
ⓓ. High electrical conductivity
Correct Answer: High Young’s modulus
Explanation: Steel’s stiffness (high Young’s modulus, $\sim 2 \times 10^{11} \, Pa$) ensures minimal elongation or bending under large loads, making it suitable for load-bearing structures.
313. Which modulus of elasticity is most important for beams under bending loads?
ⓐ. Bulk modulus
ⓑ. Shear modulus
ⓒ. Young’s modulus
ⓓ. Modulus of resilience
Correct Answer: Young’s modulus
Explanation: Beams deform mainly by bending. The amount of deflection depends on Young’s modulus, hence stiff materials are chosen.
314. In tall buildings, why is elasticity of materials carefully considered?
ⓐ. To prevent excessive vibrations and permanent deformation
ⓑ. To reduce the density of the material
ⓒ. To increase electrical insulation
ⓓ. To decrease cost of raw material
Correct Answer: To prevent excessive vibrations and permanent deformation
Explanation: Building materials must be elastic enough to withstand wind and seismic loads, ensuring reversible deformation without collapse.
315. Which of the following construction materials is most elastic in terms of modulus of elasticity?
ⓐ. Concrete ($\sim 3 \times 10^{10} \, Pa$)
ⓑ. Steel ($\sim 2 \times 10^{11} \, Pa$)
ⓒ. Timber ($\sim 1 \times 10^{10} \, Pa$)
ⓓ. Brick ($\sim 1 \times 10^{9} \, Pa$)
Correct Answer: Steel ($\sim 2 \times 10^{11} \, Pa$)
Explanation: Steel has the highest modulus among common structural materials, making it the stiffest and most elastic for engineering use.
316. Why is pre-stressed concrete used in structural engineering?
ⓐ. To reduce density of concrete
ⓑ. To improve conductivity
ⓒ. To counteract tensile stresses using pre-applied compressive stresses
ⓓ. To reduce Young’s modulus of concrete
Correct Answer: To counteract tensile stresses using pre-applied compressive stresses
Explanation: Concrete is weak in tension. Pre-stressing applies compressive stress beforehand, ensuring that under load the net tensile stress is reduced.
317. Which structural component primarily depends on shear modulus for safety design?
ⓐ. Beams
ⓑ. Columns
ⓒ. Shafts
ⓓ. Walls
Correct Answer: Shafts
Explanation: Shafts undergo torsional stresses in machinery and structural systems. Their design depends on shear modulus to resist twisting.
318. Why are aluminum alloys used in long-span roof trusses despite being less stiff than steel?
ⓐ. They are cheaper
ⓑ. They are lighter and resist corrosion
ⓒ. They have higher tensile strength
ⓓ. They are brittle
Correct Answer: They are lighter and resist corrosion
Explanation: In roof trusses, weight reduction is important. Aluminum alloys provide sufficient strength, lightness, and resistance to environmental corrosion.
319. Which of the following equations gives the deflection $\delta$ of a beam under central load $W$?
ⓐ. $\delta = \frac{WL^3}{48EI}$
ⓑ. $\delta = \frac{WL^2}{2EI}$
ⓒ. $\delta = \frac{WL}{AE}$
ⓓ. $\delta = \frac{W}{EI}$
Correct Answer: $\delta = \frac{WL^3}{48EI}$
Explanation: The central deflection of a simply supported beam under central point load $W$ is $\delta = \frac{WL^3}{48EI}$, where $E$ is Young’s modulus and $I$ is the moment of inertia.
320. Why are materials with high ductility preferred for earthquake-resistant structures?
ⓐ. They have lower thermal expansion
ⓑ. They undergo plastic deformation and absorb seismic energy
ⓒ. They are poor conductors of heat
ⓓ. They are cheaper
Correct Answer: They undergo plastic deformation and absorb seismic energy
Explanation: Ductile materials like steel deform plastically, dissipating earthquake energy and preventing sudden brittle failure, increasing safety of buildings.
321. Why is elasticity important in the manufacturing of automobile springs?
ⓐ. Springs must store and release elastic energy repeatedly
ⓑ. Springs must undergo permanent deformation
ⓒ. Springs must break under small loads
ⓓ. Springs must resist heat flow
Correct Answer: Springs must store and release elastic energy repeatedly
Explanation: Automobile springs rely on elastic behaviour to absorb shocks and vibrations. They deform under load but return to original shape, providing comfort and safety.
322. Why is mild steel preferred for making machine parts that undergo repeated loading?
ⓐ. It is brittle and fractures suddenly
ⓑ. It has low density
ⓒ. It has high elasticity and ductility
ⓓ. It has low modulus of elasticity
Correct Answer: It has high elasticity and ductility
Explanation: Mild steel shows elastic recovery under small loads and ductile plastic deformation under larger loads, ensuring safety against sudden fracture.
323. Which modulus is most relevant in designing metal sheets for stamping and deep drawing processes?
ⓐ. Bulk modulus
ⓑ. Shear modulus
ⓒ. Young’s modulus
ⓓ. Poisson’s ratio
Correct Answer: Young’s modulus
Explanation: Sheet metals must deform elastically and then plastically in controlled manner. Young’s modulus governs their elastic stiffness in these processes.
324. Why is elasticity important in the process of forging?
ⓐ. It ensures the material shatters easily
ⓑ. It ensures temporary deformation before shaping permanently
ⓒ. It prevents any deformation
ⓓ. It reduces ductility
Correct Answer: It ensures temporary deformation before shaping permanently
Explanation: During forging, materials are first elastically deformed, then plastically shaped. Elastic properties help resist cracking and distribute stress uniformly.
325. Rubber is used in manufacturing belts and couplings because:
ⓐ. It has low density
ⓑ. It has high compressibility
ⓒ. It has high elasticity and low shear modulus
ⓓ. It has high tensile strength
Correct Answer: It has high elasticity and low shear modulus
Explanation: Rubber absorbs shocks and allows slight deformations under stress, making it suitable for belts and couplings that transmit power in machines.
326. In rolling processes, why is elasticity important?
ⓐ. It determines how much thickness reduction can be permanent
ⓑ. It ensures zero deformation
ⓒ. It increases brittleness of metals
ⓓ. It avoids all shape changes
Correct Answer: It determines how much thickness reduction can be permanent
Explanation: Rolling involves elastic plus plastic deformation. Elastic recovery (spring back) after unloading must be considered for accurate thickness control.
327. Which property ensures that metallic wires can be drawn into fine wires during wire-drawing?
ⓐ. Elasticity only
ⓑ. Ductility supported by elasticity
ⓒ. Brittleness
ⓓ. Thermal conductivity
Correct Answer: Ductility supported by elasticity
Explanation: Wires are manufactured by stretching metals. Elasticity ensures temporary resistance, while ductility ensures permanent elongation without breaking.
328. Why is elasticity important in manufacturing cutting tools?
ⓐ. Tools must undergo plastic flow during cutting
ⓑ. Tools must absorb energy elastically without permanent deformation
ⓒ. Tools must shatter easily for sharpness
ⓓ. Tools must reduce Young’s modulus
Correct Answer: Tools must absorb energy elastically without permanent deformation
Explanation: Cutting tools experience large forces. Their elasticity allows recovery without damage, maintaining precision and preventing cracks.
329. Why are elastic properties of polymers studied in manufacturing packaging materials?
ⓐ. To ensure they break easily
ⓑ. To predict reversible deformations under stress
ⓒ. To increase brittleness of plastics
ⓓ. To reduce ductility of plastics
Correct Answer: To predict reversible deformations under stress
Explanation: Packaging films and containers must deform elastically under small loads and then return to shape, preventing permanent damage during handling.
330. Which modulus is critical in designing dies and molds for shaping materials?
ⓐ. Young’s modulus
ⓑ. Shear modulus
ⓒ. Bulk modulus
ⓓ. Poisson’s ratio
Correct Answer: Young’s modulus
Explanation: Dies and molds must resist high compressive and tensile stresses. A high Young’s modulus ensures they undergo minimal deformation and retain shape under repeated use.
331. Why is elasticity an important property in making sports shoes?
ⓐ. To make the shoes heavier
ⓑ. To ensure they deform plastically under load
ⓒ. To absorb shocks and return energy during movement
ⓓ. To increase friction only
Correct Answer: To absorb shocks and return energy during movement
Explanation: Elastic soles deform temporarily when the foot strikes the ground, absorbing impact energy, and then recover, improving comfort and performance.
332. Which property of materials is utilized in the design of trampolines?
ⓐ. Low Young’s modulus
ⓑ. High elasticity within limits
ⓒ. High brittleness
ⓓ. Low ductility
Correct Answer: High elasticity within limits
Explanation: Trampoline mats and springs stretch under load and then return to original shape due to their elastic behaviour, providing rebound.
333. Why is carbon fiber used in sports equipment like tennis rackets and bicycles?
ⓐ. It is brittle and fractures easily
ⓑ. It has high stiffness-to-weight ratio
ⓒ. It has very low modulus of elasticity
ⓓ. It is cheap and dense
Correct Answer: It has high stiffness-to-weight ratio
Explanation: Carbon fiber has high Young’s modulus and low density, making it stiff yet lightweight, ideal for high-performance sports equipment.
334. Which modulus is most relevant for designing helmets?
ⓐ. Bulk modulus
ⓑ. Shear modulus
ⓒ. Young’s modulus
ⓓ. Modulus of resilience
Correct Answer: Modulus of resilience
Explanation: Helmets must absorb energy from impacts elastically. Modulus of resilience (energy absorbed per unit volume in elastic range) is crucial for safety.
335. Why is elasticity important in making protective padding in sports gear?
ⓐ. To make them as stiff as possible
ⓑ. To absorb shocks by deforming elastically and recovering
ⓒ. To ensure permanent deformation
ⓓ. To increase density of the gear
Correct Answer: To absorb shocks by deforming elastically and recovering
Explanation: Protective pads must compress under impact, absorbing energy elastically, and then regain their shape for repeated use.
336. Which property of materials is essential in designing pole vaulting poles?
ⓐ. High density and brittleness
ⓑ. High elasticity and flexibility
ⓒ. Low shear modulus
ⓓ. Low tensile strength
Correct Answer: High elasticity and flexibility
Explanation: Poles must bend significantly without breaking and then release stored elastic energy to propel the vaulter upward.
337. Why is rubber used in grips of cricket bats and tennis rackets?
ⓐ. It has low elasticity
ⓑ. It absorbs shocks and vibrations elastically
ⓒ. It increases brittleness
ⓓ. It reduces friction
Correct Answer: It absorbs shocks and vibrations elastically
Explanation: Rubber grips deform elastically, absorbing shock and reducing strain on the player’s hands, while improving control.
338. In designing airbags for cars, which property is most relevant?
ⓐ. High bulk modulus
ⓑ. Elasticity and controlled energy absorption
ⓒ. High brittleness
ⓓ. Low Young’s modulus
Correct Answer: Elasticity and controlled energy absorption
Explanation: Airbags must expand elastically during collision, absorb impact energy, and cushion passengers, preventing injury.
339. Why are composite materials (like fiberglass) used in hockey sticks and skis?
ⓐ. They are brittle and fracture suddenly
ⓑ. They have high elasticity, strength, and low weight
ⓒ. They have low ductility
ⓓ. They are very dense
Correct Answer: They have high elasticity, strength, and low weight
Explanation: Composite materials combine strength and elasticity, ensuring performance with durability, while keeping equipment lightweight.
340. Which property makes elastic mouthguards effective in protecting athletes’ teeth?
ⓐ. High density
ⓑ. High elasticity and shock absorption
ⓒ. Low stiffness
ⓓ. High brittleness
Correct Answer: High elasticity and shock absorption
Explanation: Mouthguards deform elastically to absorb impact energy, reducing force transmitted to teeth and gums, then return to their original shape.
341. Why is elasticity important in the design of artificial heart valves?
ⓐ. To make them rigid and unmovable
ⓑ. To allow flexible opening and closing under blood pressure
ⓒ. To reduce density of blood
ⓓ. To increase brittleness of tissues
Correct Answer: To allow flexible opening and closing under blood pressure
Explanation: Artificial valves must deform elastically with each heartbeat, opening and closing smoothly under pressure while returning to their original shape.
342. Which modulus of elasticity is most relevant for bones under compressive loads?
ⓐ. Young’s modulus
ⓑ. Shear modulus
ⓒ. Bulk modulus
ⓓ. Modulus of rupture
Correct Answer: Young’s modulus
Explanation: Bones behave like elastic solids under stress. Young’s modulus measures stiffness and resistance to deformation, crucial in biomechanics.
343. Why is silicone rubber used in making prosthetic limbs?
ⓐ. It is brittle and light
ⓑ. It has high elasticity and flexibility
ⓒ. It has very high density
ⓓ. It has low thermal conductivity
Correct Answer: It has high elasticity and flexibility
Explanation: Silicone rubber deforms elastically under pressure, providing comfort, cushioning, and flexibility in artificial limbs.
344. Which property makes elastic catheters effective in medical applications?
ⓐ. Low density
ⓑ. Ability to bend and recover shape without breaking
ⓒ. High brittleness
ⓓ. High conductivity
Correct Answer: Ability to bend and recover shape without breaking
Explanation: Catheters must bend inside the body without permanent deformation, which requires high elasticity and toughness.
345. In biomechanics, tendons and ligaments are modeled as:
ⓐ. Perfectly rigid materials
ⓑ. Elastic bodies that store and release strain energy
ⓒ. Brittle solids with no elasticity
ⓓ. Fluids with no resistance
Correct Answer: Elastic bodies that store and release strain energy
Explanation: Tendons and ligaments deform elastically under stress, storing strain energy and aiding in efficient body movement.
346. Why is elasticity important in stents used to open blocked arteries?
ⓐ. They must remain rigid and inflexible
ⓑ. They must expand elastically to fit inside arteries
ⓒ. They must reduce Young’s modulus of blood
ⓓ. They must resist all deformation
Correct Answer: They must expand elastically to fit inside arteries
Explanation: Stents are designed to expand under pressure and hold open arteries. Elastic deformation ensures they adapt to vessel walls without breaking.
347. Which property of cartilage makes it suitable as a shock absorber in joints?
ⓐ. High bulk modulus and elastic recovery
ⓑ. High brittleness
ⓒ. High tensile strength only
ⓓ. Very low Young’s modulus
Correct Answer: High bulk modulus and elastic recovery
Explanation: Cartilage deforms under load, absorbing shocks, and then regains shape elastically, protecting bones in joints.
348. Why is titanium alloy used in bone implants?
ⓐ. It has low density and poor strength
ⓑ. It has high elasticity, biocompatibility, and similar modulus to bone
ⓒ. It is brittle like glass
ⓓ. It cannot deform elastically
Correct Answer: It has high elasticity, biocompatibility, and similar modulus to bone
Explanation: Titanium alloys provide the right stiffness (Young’s modulus close to bone), resist corrosion, and are biocompatible, making them ideal for implants.
349. Which modulus is most relevant in studying deformation of blood vessels under blood pressure?
ⓐ. Bulk modulus
ⓑ. Young’s modulus
ⓒ. Shear modulus
ⓓ. Modulus of rupture
Correct Answer: Young’s modulus
Explanation: Blood vessels deform under tensile stresses from internal pressure. Their elasticity is characterized by Young’s modulus.
350. Why are viscoelastic models used in biomechanics instead of purely elastic models?
ⓐ. Biological tissues only store energy
ⓑ. Biological tissues exhibit both elastic and time-dependent viscous behaviour
ⓒ. Biological tissues are perfectly rigid
ⓓ. Biological tissues cannot deform
Correct Answer: Biological tissues exhibit both elastic and time-dependent viscous behaviour
Explanation: Tissues like muscles, ligaments, and skin are viscoelastic — they deform elastically under stress but also show time-dependent flow, requiring viscoelastic models in biomechanics.
351. What is plastic deformation?
ⓐ. Temporary change in shape of a material under stress
ⓑ. Permanent change in shape of a material after removal of stress
ⓒ. Elastic recovery of a body
ⓓ. Vibration of atoms under stress
Correct Answer: Permanent change in shape of a material after removal of stress
Explanation: Plastic deformation occurs when a material is stressed beyond its elastic limit. Unlike elastic deformation, it is irreversible, and the material does not return to its original shape.
352. Which point on the stress–strain curve marks the beginning of plastic deformation?
ⓐ. Proportional limit
ⓑ. Elastic limit
ⓒ. Yield point
ⓓ. Breaking point
Correct Answer: Yield point
Explanation: At the yield point, the material transitions from elastic to plastic behaviour. Beyond this, deformation becomes permanent.
353. Which of the following is a characteristic of plastic deformation?
ⓐ. Fully reversible deformation
ⓑ. Stress and strain are directly proportional
ⓒ. Irreversible deformation beyond elastic limit
ⓓ. Material breaks immediately at elastic limit
Correct Answer: Irreversible deformation beyond elastic limit
Explanation: Plastic deformation is irreversible. Stress and strain lose linear proportionality, and permanent deformation occurs.
354. Why is plastic deformation important in manufacturing processes?
ⓐ. It helps materials resist all stress
ⓑ. It allows materials to be shaped into wires, sheets, and components
ⓒ. It makes materials brittle
ⓓ. It reduces ductility
Correct Answer: It allows materials to be shaped into wires, sheets, and components
Explanation: Processes like forging, rolling, and drawing depend on plastic deformation, where permanent shape change is required.
355. Which type of materials generally exhibit significant plastic deformation before fracture?
ⓐ. Brittle materials like glass
ⓑ. Ductile materials like copper and steel
ⓒ. Ceramics
ⓓ. Graphite
Correct Answer: Ductile materials like copper and steel
Explanation: Ductile materials undergo large plastic deformation before breaking, making them safer for engineering use. Brittle materials fracture without noticeable plasticity.
356. Plastic deformation is accompanied by which atomic process?
ⓐ. Perfectly elastic stretching of bonds
ⓑ. Permanent slip and dislocation movement of atoms
ⓒ. Vibrations only
ⓓ. No change in atomic arrangement
Correct Answer: Permanent slip and dislocation movement of atoms
Explanation: Plastic deformation arises when dislocations move and atoms permanently rearrange, unlike reversible elastic deformation caused by bond stretching.
357. Which equation represents strain in plastic region?
ⓐ. $\epsilon = \sigma / E$
ⓑ. $\epsilon = \sigma^2 / E$
ⓒ. No linear relation, depends on yield and hardening properties
ⓓ. $\epsilon = 0$
Correct Answer: No linear relation, depends on yield and hardening properties
Explanation: In the plastic region, Hooke’s law fails. The stress–strain relation becomes non-linear, depending on strain hardening and material properties.
358. What is the main difference between elastic and plastic deformation?
ⓐ. Elastic deformation is permanent, plastic deformation is temporary
ⓑ. Elastic deformation is reversible, plastic deformation is irreversible
ⓒ. Both are fully reversible
ⓓ. Both are irreversible
Correct Answer: Elastic deformation is reversible, plastic deformation is irreversible
Explanation: Elastic deformation allows full recovery of shape, while plastic deformation causes permanent structural changes.
359. Which phenomenon occurs if a metal wire is stretched beyond its elastic limit?
ⓐ. It breaks instantly
ⓑ. It undergoes plastic deformation and elongates permanently
ⓒ. It vibrates but regains shape
ⓓ. It contracts suddenly
Correct Answer: It undergoes plastic deformation and elongates permanently
Explanation: Beyond elastic limit, metals do not regain original length. Permanent elongation occurs due to plastic flow.
360. Why is knowledge of plastic deformation essential in engineering design?
ⓐ. To make all materials perfectly elastic
ⓑ. To predict failure loads and safe working limits
ⓒ. To ignore stress–strain curve
ⓓ. To design brittle materials only
Correct Answer: To predict failure loads and safe working limits
Explanation: Engineers must know the extent of plastic deformation to avoid permanent structural damage and ensure safety in design.
361. What is meant by plastic flow in materials?
ⓐ. Temporary change in dimensions under load
ⓑ. Continuous and permanent deformation of a material under constant stress
ⓒ. Elastic recovery after stress removal
ⓓ. Sudden fracture without warning
Correct Answer: Continuous and permanent deformation of a material under constant stress
Explanation: Plastic flow is the permanent movement of atoms or dislocations under sustained stress beyond elastic limit. The material does not return to original shape when stress is removed.
362. Which phenomenon is associated with plastic flow in metals?
ⓐ. Dislocation motion and slip of atomic planes
ⓑ. Elastic stretching of bonds
ⓒ. Sudden shattering of bonds
ⓓ. No change in atomic arrangement
Correct Answer: Dislocation motion and slip of atomic planes
Explanation: Plastic flow in metals occurs mainly due to dislocation movement, which allows planes of atoms to slide past each other permanently.
363. What type of deformation is observed in lead when subjected to small stress?
ⓐ. Purely elastic
ⓑ. Elastic followed by plastic flow
ⓒ. No deformation
ⓓ. Only brittle fracture
Correct Answer: Elastic followed by plastic flow
Explanation: Lead and other soft metals exhibit plastic flow even under small stresses, showing high ductility and permanent deformation.
364. Which of the following best describes permanent deformation?
ⓐ. Deformation fully recovered after unloading
ⓑ. Deformation that remains after stress is removed
ⓒ. Deformation with no change in shape
ⓓ. Deformation that disappears instantly
Correct Answer: Deformation that remains after stress is removed
Explanation: Permanent deformation occurs once the elastic limit is exceeded, and plastic flow ensures the material retains some altered shape after load removal.
365. What is the main cause of permanent deformation in crystalline solids?
ⓐ. Vibration of atoms only
ⓑ. Dislocation slip and twinning
ⓒ. Magnetic domain alignment
ⓓ. Thermal expansion
Correct Answer: Dislocation slip and twinning
Explanation: In crystalline solids, plastic flow and permanent deformation are primarily due to dislocation slip and sometimes twinning of crystal planes.
366. Which equation best describes permanent strain after yielding?
ⓐ. $\epsilon = \frac{\sigma}{E}$
ⓑ. $\epsilon = \epsilon_e + \epsilon_p$
ⓒ. $\epsilon = \sigma^2/E$
ⓓ. $\epsilon = 0$
Correct Answer: $\epsilon = \epsilon_e + \epsilon_p$
Explanation: Total strain is the sum of elastic strain $\epsilon_e$ (recoverable) and plastic strain $\epsilon_p$ (permanent). Plastic strain remains after unloading.
367. Which characteristic differentiates plastic flow from creep?
ⓐ. Plastic flow occurs under short-term loading; creep occurs under long-term loading
ⓑ. Plastic flow depends on temperature; creep does not
ⓒ. Plastic flow is fully reversible; creep is irreversible
ⓓ. Plastic flow requires zero stress; creep requires infinite stress
Correct Answer: Plastic flow occurs under short-term loading; creep occurs under long-term loading
Explanation: Plastic flow occurs when stress exceeds elastic limit in short time, while creep is slow, time-dependent deformation under constant stress.
368. In forming processes like rolling and forging, permanent deformation is achieved by:
ⓐ. Elastic stretching of bonds
ⓑ. Controlled plastic flow
ⓒ. Sudden fracture
ⓓ. Reducing ductility
Correct Answer: Controlled plastic flow
Explanation: Rolling, forging, and extrusion rely on plastic flow of materials, allowing permanent shaping into useful components.
369. Which of the following materials exhibits significant plastic flow before failure?
ⓐ. Glass
ⓑ. Mild steel
ⓒ. Cast iron
ⓓ. Concrete
Correct Answer: Mild steel
Explanation: Mild steel is ductile and undergoes large plastic deformation (plastic flow) before fracture. Brittle materials like glass and cast iron show little or none.
370. Why is study of permanent deformation important in engineering?
ⓐ. To make materials always elastic
ⓑ. To design forming processes and ensure structures do not fail under overload
ⓒ. To eliminate use of metals in industry
ⓓ. To reduce material cost only
Correct Answer: To design forming processes and ensure structures do not fail under overload
Explanation: Knowledge of permanent deformation helps engineers predict safe load limits, design forming operations (forging, rolling), and prevent unexpected structural failures.
371. How does increasing temperature generally affect plastic deformation in metals?
ⓐ. It makes metals more brittle
ⓑ. It decreases ductility
ⓒ. It increases ductility and ease of plastic flow
ⓓ. It prevents dislocation movement
Correct Answer: It increases ductility and ease of plastic flow
Explanation: At higher temperatures, atomic vibrations increase, making dislocation movement easier. Metals deform more plastically, showing greater ductility.
372. Which factor causes metals to become brittle at low temperatures?
ⓐ. High density
ⓑ. Reduced dislocation mobility
ⓒ. Increased bulk modulus
ⓓ. Higher electrical conductivity
Correct Answer: Reduced dislocation mobility
Explanation: At low temperatures, atomic vibrations are restricted, making dislocation motion harder. This leads to brittle fracture instead of plastic flow.
373. Why are metals heated before forging or rolling?
ⓐ. To increase density
ⓑ. To reduce ductility
ⓒ. To improve plastic deformation by reducing yield stress
ⓓ. To reduce modulus of elasticity
Correct Answer: To improve plastic deformation by reducing yield stress
Explanation: Heating lowers yield strength and facilitates dislocation movement, allowing metals to undergo plastic deformation more easily during forging or rolling.
374. How does the rate of loading affect plastic deformation?
ⓐ. Slow loading reduces plastic deformation
ⓑ. Fast loading promotes ductile flow
ⓒ. Slow loading allows greater plastic deformation; fast loading increases brittleness
ⓓ. Rate of loading has no effect
Correct Answer: Slow loading allows greater plastic deformation; fast loading increases brittleness
Explanation: Under slow loading, dislocations have time to move, allowing plastic deformation. Under fast loading, dislocations cannot move quickly, causing brittle fracture.
375. Which of the following explains why glass shatters under impact but may deform under slow pressure?
ⓐ. Glass has high ductility
ⓑ. Glass is highly elastic at all times
ⓒ. Rate of loading influences fracture behaviour
ⓓ. Glass has high tensile strength
Correct Answer: Rate of loading influences fracture behaviour
Explanation: Brittle materials like glass may fail under sudden loading due to high stress concentration, while under slow loading, they may undergo limited deformation.
376. At high strain rates, metals tend to:
ⓐ. Show higher ductility
ⓑ. Behave more brittle
ⓒ. Lower their yield stress significantly
ⓓ. Remain unchanged in behaviour
Correct Answer: Behave more brittle
Explanation: At high strain rates (fast loading), dislocation motion is restricted, leading to reduced plastic flow and brittle-like fracture.
377. Why is hot rolling of steel easier than cold rolling?
ⓐ. Because steel density decreases at high temperature
ⓑ. Because steel’s elastic modulus increases at high temperature
ⓒ. Because yield stress decreases at high temperature, enhancing plastic deformation
ⓓ. Because steel becomes brittle at high temperature
Correct Answer: Because yield stress decreases at high temperature, enhancing plastic deformation
Explanation: At elevated temperature, steel’s yield strength reduces, making plastic deformation easier in hot rolling compared to cold rolling.
378. Which of the following is an effect of low temperature on plastic deformation?
ⓐ. Lower yield strength
ⓑ. Higher ductility
ⓒ. Increase in brittleness
ⓓ. Increase in dislocation motion
Correct Answer: Increase in brittleness
Explanation: Low temperature restricts atomic motion and dislocation mobility. Materials lose ductility and show brittle fracture.
379. Which factor is most critical in determining whether a material exhibits ductile or brittle fracture?
ⓐ. Density
ⓑ. Elastic limit
ⓒ. Temperature and strain rate
ⓓ. Poisson’s ratio
Correct Answer: Temperature and strain rate
Explanation: Materials tend to be more ductile at higher temperatures and lower strain rates, and more brittle at low temperatures and high strain rates.
380. Why is annealing done after cold working?
ⓐ. To decrease plasticity
ⓑ. To remove residual stresses and restore ductility
ⓒ. To increase brittleness
ⓓ. To permanently harden the material
Correct Answer: To remove residual stresses and restore ductility
Explanation: Cold working increases dislocation density, reducing ductility. Annealing relieves internal stresses and restores plastic deformation capacity.
381. Which everyday example demonstrates plastic deformation?
ⓐ. Stretching a rubber band within limits
ⓑ. Permanent bending of a paperclip
ⓒ. Oscillations of a spring
ⓓ. Compression of air in a cylinder
Correct Answer: Permanent bending of a paperclip
Explanation: A paperclip, when bent beyond its elastic limit, undergoes plastic deformation and does not return to its original shape.
382. Why is plastic deformation important in the process of metal forming?
ⓐ. It prevents any change in material shape
ⓑ. It allows permanent shaping of metals into sheets, wires, and rods
ⓒ. It increases elasticity of metals
ⓓ. It avoids ductility
Correct Answer: It allows permanent shaping of metals into sheets, wires, and rods
Explanation: Manufacturing processes like forging, rolling, and extrusion rely on plastic deformation for shaping metals permanently.
383. Drawing copper into wires is possible because:
ⓐ. Copper is brittle
ⓑ. Copper is highly ductile and undergoes plastic deformation
ⓒ. Copper has low Young’s modulus
ⓓ. Copper has high brittleness
Correct Answer: Copper is highly ductile and undergoes plastic deformation
Explanation: Copper can undergo significant plastic deformation without breaking, allowing it to be drawn into fine wires.
384. Which application uses controlled plastic deformation of metals?
ⓐ. Elastic springs
ⓑ. Forging and stamping of automobile parts
ⓒ. Oscillations in pendulums
ⓓ. Sound wave propagation
Correct Answer: Forging and stamping of automobile parts
Explanation: Automobile components are manufactured by controlled plastic deformation processes like forging, stamping, and pressing.
385. What kind of deformation is observed in clay when molded into bricks?
ⓐ. Elastic deformation only
ⓑ. Plastic deformation
ⓒ. Vibrational deformation
ⓓ. No deformation
Correct Answer: Plastic deformation
Explanation: Clay undergoes plastic deformation when molded, retaining the new shape permanently after stress removal.
386. Why do blacksmiths heat metal before hammering it into shape?
ⓐ. To decrease its elasticity
ⓑ. To improve plastic deformation by reducing yield strength
ⓒ. To increase brittleness
ⓓ. To increase Young’s modulus
Correct Answer: To improve plastic deformation by reducing yield strength
Explanation: Heating reduces the metal’s yield strength, making it easier to shape permanently under hammering.
387. Which application of plastic deformation is used in the creation of aluminum foils?
ⓐ. Elastic deformation of sheets
ⓑ. Plastic deformation through rolling
ⓒ. Sudden fracture of sheets
ⓓ. Elastic vibration of sheets
Correct Answer: Plastic deformation through rolling
Explanation: Aluminum foils are produced by rolling aluminum sheets until they undergo permanent thickness reduction via plastic flow.
388. Which process of manufacturing depends directly on plastic deformation of metals?
ⓐ. Rolling, extrusion, and forging
ⓑ. Elastic oscillations
ⓒ. Heat conduction
ⓓ. Magnetic alignment
Correct Answer: Rolling, extrusion, and forging
Explanation: These processes permanently shape metals using controlled plastic deformation, not temporary elastic behaviour.
389. Why is ductile plastic deformation preferred in structural materials?
ⓐ. It increases risk of sudden failure
ⓑ. It provides warning before fracture through visible elongation
ⓒ. It reduces strength of material
ⓓ. It makes materials brittle
Correct Answer: It provides warning before fracture through visible elongation
Explanation: Ductile materials undergo large plastic deformation before failure, giving engineers warning to prevent catastrophic collapse.
390. Which application of plastic deformation is observed in earthquake-resistant building design?
ⓐ. Elastic oscillations of columns
ⓑ. Plastic hinges forming in beams to dissipate energy
ⓒ. Perfectly elastic recovery of beams
ⓓ. Permanent brittleness of materials
Correct Answer: Plastic hinges forming in beams to dissipate energy
Explanation: In earthquake-resistant design, structures are allowed to form plastic hinges at certain points, absorbing seismic energy and preventing sudden collapse.
391. What is strain hardening?
ⓐ. Increase in brittleness of a material under stress
ⓑ. Increase in strength and hardness of a material due to plastic deformation
ⓒ. Decrease in tensile strength after elastic limit
ⓓ. Reduction of ductility under heating
Correct Answer: Increase in strength and hardness of a material due to plastic deformation
Explanation: Strain hardening (or work hardening) is the phenomenon where a material becomes stronger and harder after undergoing plastic deformation because of increased dislocation density.
392. What is the primary mechanism of strain hardening in metals?
ⓐ. Decrease in Young’s modulus
ⓑ. Increase in dislocation density and entanglement
ⓒ. Elastic bond stretching only
ⓓ. Reduction in atomic mass
Correct Answer: Increase in dislocation density and entanglement
Explanation: During plastic deformation, dislocations multiply and entangle, hindering their further motion. This increases the stress required for additional deformation, strengthening the material.
393. Which region of the stress–strain curve shows strain hardening?
ⓐ. Elastic region
ⓑ. Plastic region after yield point and before UTS
ⓒ. Proportional limit
ⓓ. Breaking point
Correct Answer: Plastic region after yield point and before UTS
Explanation: Strain hardening occurs after yield point, where the material continues to deform plastically but requires increasing stress up to ultimate tensile strength.
394. Which type of materials typically show strain hardening?
ⓐ. Brittle materials like glass
ⓑ. Ductile metals like copper and aluminum
ⓒ. Ceramics
ⓓ. Concrete
Correct Answer: Ductile metals like copper and aluminum
Explanation: Ductile metals undergo strain hardening during plastic deformation. Brittle materials usually fracture before significant strain hardening can occur.
395. Which of the following statements is correct about strain hardening?
ⓐ. It reduces tensile strength
ⓑ. It increases hardness and yield strength
ⓒ. It reduces resistance to further deformation
ⓓ. It increases ductility
Correct Answer: It increases hardness and yield strength
Explanation: Strain hardening strengthens the material, raising both yield strength and hardness, but usually decreases ductility.
396. Why does ductility decrease during strain hardening?
ⓐ. Because dislocations annihilate
ⓑ. Because dislocations accumulate and restrict plastic flow
ⓒ. Because atomic bonds weaken
ⓓ. Because density increases drastically
Correct Answer: Because dislocations accumulate and restrict plastic flow
Explanation: High dislocation density restricts slip, making further plastic deformation harder. This reduces ductility while increasing strength.
397. Which formula best represents the true stress during strain hardening?
ⓐ. $\sigma = K \epsilon^n$
ⓑ. $\sigma = E \cdot \epsilon$
ⓒ. $\sigma = \frac{F}{A_0}$
ⓓ. $\sigma = Y \cdot \epsilon^2$
Correct Answer: $\sigma = K \epsilon^n$
Explanation: In strain hardening, true stress ($\sigma$) follows a power-law relation with strain: $\sigma = K \epsilon^n$, where $n$ is the strain-hardening exponent.
398. If the strain-hardening exponent $n$ of a material is high, what does it indicate?
ⓐ. Material cannot deform plastically
ⓑ. Material has strong ability to strain harden, increasing strength with deformation
ⓒ. Material fractures without warning
ⓓ. Material has very low yield point
Correct Answer: Material has strong ability to strain harden, increasing strength with deformation
Explanation: Higher $n$ means greater strengthening during plastic deformation. Such materials can sustain larger plastic strains without fracture.
399. Why is cold working directly associated with strain hardening?
ⓐ. Cold working increases dislocation density without recovery
ⓑ. Cold working removes dislocations completely
ⓒ. Cold working increases Young’s modulus
ⓓ. Cold working makes materials brittle like glass
Correct Answer: Cold working increases dislocation density without recovery
Explanation: At low temperatures, dislocations cannot rearrange or annihilate easily. This accumulates dislocations, causing strain hardening.
400. What is one practical application of strain hardening?
ⓐ. Drawing copper into thin wires with higher strength
ⓑ. Making glass more ductile
ⓒ. Reducing yield strength of steel
ⓓ. Increasing plasticity of ceramics
Correct Answer: Drawing copper into thin wires with higher strength
Explanation: Copper wires and sheets are strengthened by strain hardening during drawing and rolling, increasing strength without adding extra material.
The topic Mechanical Properties of Solids is essential in Class 11 Physics (NCERT/CBSE syllabus), helping students understand how different materials behave under stress and strain. It is a scoring topic in board exams and highly significant for competitive exams such as JEE, NEET, and other entrance tests. With a total of 560 MCQs divided into 6 parts, this chapter offers extensive practice. In Part 4, you will solve the fourth set of 100 questions, which includes concept-based and numerical problems for advanced preparation.
- 👉 Total MCQs in this chapter: 560.
- 👉 This page contains: Fourth set of 100 solved MCQs.
- 👉 Very helpful for board exams and competitive exams.
- 👉 To see MCQs from other chapters, use the top navigation bar.
- 👉 Next, move on to the Part 5 button above for more questions.