Chapter 8: Mechanical Properties of Solids Assertion-Reason Questions | physics Class 11 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Stress has the same SI unit as pressure. Reason (R): Both stress and pressure are defined as force per unit area.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Strain has no units or dimensional formula. Reason (R): Strain is a ratio of two quantities having the same dimensions.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Steel is more elastic than rubber. Reason (R): Steel has a higher Young's modulus than rubber and requires a larger force to produce the same strain.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): Hooke's law is valid for all materials under any magnitude of applied force. Reason (R): Hooke's law is an empirical law that holds only for small deformations within the proportional limit.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The Young's modulus and shear modulus are relevant only for solids. Reason (R): Only solids have a definite shape and length; fluids cannot sustain shear stress or support a change in length.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Bulk modulus is relevant for solids, liquids, and gases. Reason (R): All three states of matter undergo changes in volume when subjected to uniform pressure from all sides.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): Gases are about a million times more compressible than solids. Reason (R): Molecules in gases are very poorly coupled to their neighbours, whereas atoms in solids are tightly bound.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): A material which stretches more for a given load is considered more elastic in daily life. Reason (R): Scientifically, a material with a higher Young's modulus that stretches less for the same load is more elastic.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): The yield point and elastic limit refer to the same point B on the stress-strain curve. Reason (R): Beyond point B, the material does not return to its original shape and undergoes plastic deformation.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Increasing the depth of a beam is more effective than increasing its breadth in reducing sag. Reason (R): In the sag formula δ = Wl³/(4bd³Y), sag is proportional to d⁻³ but only to b⁻¹.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): Glass is ductile while brass is brittle. Reason (R): In a ductile material, the ultimate tensile strength point and the fracture point are far apart on the stress-strain curve.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): The elastic potential energy stored per unit volume of a stretched wire is ½σε. Reason (R): When a wire is stretched, work done against inter-atomic forces is stored as elastic potential energy.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 13

Logic Check

Assertion (A): The tensile stress in a wire suspended from the ceiling and supporting a weight F at its lower end is F/A. Reason (R): The tension at any cross-section of the wire is F (not 2F), as only one end carries the applied weight.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): Shear modulus is generally less than Young's modulus for the same material. Reason (R): For most materials, G ≈ Y/3, meaning it is easier to change the shape of a material (shear) than its length (longitudinal deformation).

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 15

Logic Check

Assertion (A): Elastomers like rubber do not obey Hooke's law. Reason (R): Elastomers have a non-linear stress-strain relationship over most of their elastic range and have no well-defined proportional limit.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 16

Logic Check

Assertion (A): Crane ropes are made of many thin wires braided together rather than a single thick wire. Reason (R): A single thick wire of the required load-bearing radius would be too rigid to wind on a drum or pass over pulleys.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): Hydraulic stress changes the volume of a body without changing its shape. Reason (R): In hydraulic stress, forces act perpendicular to every point on the surface uniformly, causing isotropic (uniform in all directions) compression.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): The maximum height of a mountain on Earth is estimated to be about 10 km. Reason (R): This is because the bulk modulus of rock is exceeded at greater heights, causing rock to flow.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 19

Logic Check

Assertion (A): Poisson's ratio is a dimensionless quantity. Reason (R): Poisson's ratio is the ratio of lateral strain to longitudinal strain, both of which are dimensionless.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 20

Logic Check

Assertion (A): Steel is preferred over aluminium in heavy-duty structural designs. Reason (R): Steel has a higher Young's modulus (200 GPa) than aluminium (70 GPa), meaning steel resists deformation more strongly for the same applied stress.

Reasoning Options

ByteNotes

Chapter sections

Chapter 8: Mechanical Properties of Solids | Assertion-Reason

Assertion (A): Stress has the same SI unit as pressure. Reason (R): Both stress and pressure are defined as force per unit area.

Assertion (A): Strain has no units or dimensional formula. Reason (R): Strain is a ratio of two quantities having the same dimensions.

Assertion (A): Steel is more elastic than rubber. Reason (R): Steel has a higher Young's modulus than rubber and requires a larger force to produce the same strain.

Assertion (A): Hooke's law is valid for all materials under any magnitude of applied force. Reason (R): Hooke's law is an empirical law that holds only for small deformations within the proportional limit.

Assertion (A): The Young's modulus and shear modulus are relevant only for solids. Reason (R): Only solids have a definite shape and length; fluids cannot sustain shear stress or support a change in length.

Assertion (A): Bulk modulus is relevant for solids, liquids, and gases. Reason (R): All three states of matter undergo changes in volume when subjected to uniform pressure from all sides.

Assertion (A): Gases are about a million times more compressible than solids. Reason (R): Molecules in gases are very poorly coupled to their neighbours, whereas atoms in solids are tightly bound.

Assertion (A): A material which stretches more for a given load is considered more elastic in daily life. Reason (R): Scientifically, a material with a higher Young's modulus that stretches less for the same load is more elastic.

Assertion (A): The yield point and elastic limit refer to the same point B on the stress-strain curve. Reason (R): Beyond point B, the material does not return to its original shape and undergoes plastic deformation.

Assertion (A): Increasing the depth of a beam is more effective than increasing its breadth in reducing sag. Reason (R): In the sag formula δ = Wl³/(4bd³Y), sag is proportional to d⁻³ but only to b⁻¹.

Assertion (A): Glass is ductile while brass is brittle. Reason (R): In a ductile material, the ultimate tensile strength point and the fracture point are far apart on the stress-strain curve.

Assertion (A): The elastic potential energy stored per unit volume of a stretched wire is ½σε. Reason (R): When a wire is stretched, work done against inter-atomic forces is stored as elastic potential energy.

Assertion (A): The tensile stress in a wire suspended from the ceiling and supporting a weight F at its lower end is F/A. Reason (R): The tension at any cross-section of the wire is F (not 2F), as only one end carries the applied weight.

Assertion (A): Shear modulus is generally less than Young's modulus for the same material. Reason (R): For most materials, G ≈ Y/3, meaning it is easier to change the shape of a material (shear) than its length (longitudinal deformation).

Assertion (A): Elastomers like rubber do not obey Hooke's law. Reason (R): Elastomers have a non-linear stress-strain relationship over most of their elastic range and have no well-defined proportional limit.

Assertion (A): Crane ropes are made of many thin wires braided together rather than a single thick wire. Reason (R): A single thick wire of the required load-bearing radius would be too rigid to wind on a drum or pass over pulleys.

Assertion (A): Hydraulic stress changes the volume of a body without changing its shape. Reason (R): In hydraulic stress, forces act perpendicular to every point on the surface uniformly, causing isotropic (uniform in all directions) compression.

Assertion (A): The maximum height of a mountain on Earth is estimated to be about 10 km. Reason (R): This is because the bulk modulus of rock is exceeded at greater heights, causing rock to flow.

Assertion (A): Poisson's ratio is a dimensionless quantity. Reason (R): Poisson's ratio is the ratio of lateral strain to longitudinal strain, both of which are dimensionless.

Assertion (A): Steel is preferred over aluminium in heavy-duty structural designs. Reason (R): Steel has a higher Young's modulus (200 GPa) than aluminium (70 GPa), meaning steel resists deformation more strongly for the same applied stress.

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