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All questions of Mechanical Properties of Solids for NEET Exam

Material is said to be ductile if
  • a)
    a large amount of plastic deformation takes place between the elastic limit and the fracture point
  • b)
    fracture occurs soon after the elastic limit is passed
  • c)
    material cross section is not significantly reduced at failure
  • d)
    material breaks suddenly at little elongation
Correct answer is option 'A'. Can you explain this answer?

Nandini Iyer answered
A ductile material is one that can withstand a large amount of plastic deformation between the elastic limit and the fracture point.
A material that breaks suddenly when elongated or fracture occurs in it soon after the elastic limit is crossed is called a brittle material.
A ductile material that exhibits extra elongation or deformation and does not fracture is also referred as superplastic material.

Putty or mud is an example of
  • a)
    semi elastic
  • b)
    plastic material
  • c)
    elastomers
  • d)
    elastic material
Correct answer is option 'B'. Can you explain this answer?

New Words answered
Since mud or putty have no gross tendency to regain their previous shape & they get permanently deformed, they are close to ideal plastics.
  1. Perfectly plastic bodies are those that retain their distorted shape or size after external pressures applied to them have been released.
  2. Partially elastic bodies are those that partially return to their former shape or size when external forces are eliminated.
  3. The shape or size of mud or putty is now altered when force is applied, and the body does not return to its original state when the force is removed. Only perfectly plastic bodies, as already established, exhibit this feature.
  4. Additionally, many elasticity moduli types are used to measure elasticity.
  5. The ratio of stress to strain given to a body under various variations in dimension is what makes up an elastic modulus.
  6. Young's Modulus, Shear Modulus, and Bulk Modulus are the three forms of elastic moduli. Since Young's modulus or longitudinal stress by strain for mud or putty is almost zero, they are theoretically proven to be almost ideal plastic bodies.
Hence, putty or mud is an example of a perfectly plastic body.

Which of the following represents Hooke’s Law?
  • a)
    Stress = k x strain
  • b)
  • c)
    Stress = k x (strain)2
  • d)
    Stress2 = k x strain
Correct answer is option 'A'. Can you explain this answer?

Gaurav Kumar answered
The  law states that the strain in a solid is proportional to the applied stress within the elastic limit of that solid body i.e. stress = k x strain.

You hang a flood lamp from the end of a vertical steel wire. The flood lamp stretches the wire 0.18 mm and the stress is proportional to the strain. How much would it have stretched if the wire had the same length but twice the diameter?
  • a)
    0.065 mm
  • b)
    0.055 mm
  • c)
    0.045 mm
  • d)
    0.075 mm
Correct answer is option 'C'. Can you explain this answer?

Pritam Kapoor answered
Given:
- The flood lamp stretches the wire by 0.18 mm
- The stress is proportional to the strain
To find:
- How much would it have stretched if the wire had the same length but twice the diameter

Let's begin by understanding the given information.

Stress is defined as the force per unit area and is denoted by the symbol σ (sigma). Mathematically, stress is given by:

σ = F / A

where F is the force applied and A is the area over which the force is applied.

Strain is defined as the change in length per unit length and is denoted by the symbol ε (epsilon). Mathematically, strain is given by:

ε = ΔL / L

where ΔL is the change in length and L is the original length.

From the given information, we know that the stress is proportional to the strain. This can be expressed mathematically as:

σ ∝ ε

or

σ = kε

where k is a constant of proportionality.

Now, let's apply this information to the problem at hand.

When the flood lamp is hung from the wire, it exerts a force on the wire which causes it to stretch. Let's assume that the original diameter of the wire is d and the original length is L.

From the given information, we know that the stress is proportional to the strain. Therefore, we can write:

σ = kε

where σ is the stress, k is a constant of proportionality, and ε is the strain.

The stress can be calculated using the formula:

σ = F / A

where F is the force applied and A is the cross-sectional area of the wire.

The force applied is the weight of the flood lamp, which can be calculated using the formula:

F = mg

where m is the mass of the flood lamp and g is the acceleration due to gravity.

The cross-sectional area of the wire can be calculated using the formula:

A = πd^2 / 4

where d is the diameter of the wire.

Therefore, we can write:

σ = (mg) / (πd^2 / 4)

The strain can be calculated using the formula:

ε = ΔL / L

where ΔL is the change in length and L is the original length.

From the given information, we know that the flood lamp stretches the wire by 0.18 mm. Therefore, we can write:

ε = 0.18 / L

Now, let's combine the equations for stress and strain:

σ = kε

σ = (mg) / (πd^2 / 4)

ε = 0.18 / L

Substituting the values of σ and ε, we get:

(mg) / (πd^2 / 4) = k (0.18 / L)

Simplifying, we get:

k = (mgL) / (0.18πd^2)

Now, let's use this value of k to calculate the change in length when the diameter of the wire is doubled.

When the diameter of the wire is doubled, the cross-sectional area of the wire becomes 4 times the original area. Therefore, the new diameter is 2d and the new cross-sectional area is:

A' = π(2d)^2 / 4 = 4πd^2

Using the same formula for stress,

What diameter should a 10-m-long steel wire have if we do not want it to stretch more than 0.5 cm under a tension of 940 N? Take Young's modulus of steel as 20 × 1010 Pa
  • a)
    3.2 mm
  • b)
    3.0 mm
  • c)
    3.4 mm
  • d)
    3.6 mm
Correct answer is option 'C'. Can you explain this answer?

Rajesh Gupta answered
Y=F x l/A x Δ l
Δ l=0.5cm=0.5x10-2m, l=10M, F=940N
Y=20x1010pa
20x1010=940x10/πr2x0.5x10-10
πr2=94x100/5x10-3x2x1011=94x102/10x108
r2=94/π x 10-7 =2.99 x 10-6
r2 ≅3x10-6
r=1.13x10-10 m
diameter=2r=3.6mm

With reference to figure the elastic zone is
  • a)
    BC
  • b)
    CD
  • c)
    AB
  • d)
    OA
Correct answer is option 'D'. Can you explain this answer?

Hansa Sharma answered
Hooke’s law: a law stating that the strain in a solid is proportional to the applied stress within the elastic limit of that solid.
In the OA line Hooke’s law is valid because stress is directly proportional to strain.

The modulus of elasticity of steel is greater than that of rubber because under the same stress
  • a)
    the strain in steel is less than rubber
  • b)
    the strain in steel is more than rubber
  • c)
    elongation in steel is more than in rubber
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Om Desai answered
Modulus of elasticity= stress/strain =(F/A)/(ΔL/L) So, for same stress Modulus of elasticity ∝( L/ΔL)and ΔL for rubber is more as compared to steel so Modulus of elasticity for rubber will be less as they are inversely proportional and also ΔL/L is less for steel

The S.I unit of stress is
  • a)
    Watt
  • b)
    Joule
  • c)
    Pascal
  • d)
    Newton
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
Stress has its own SI unit called the Pascal. 1 Pascal (Pa) is equal to 1 N/m2. In imperial units stress is measured in pound force per square inch which is often shortened to "psi". The dimension of stress is same as that of pressure.

A solid cylinder can be subjected to
  • a)
    tensile stress
  • b)
    compressive stress
  • c)
    shearing stress
  • d)
    all the above
Correct answer is option 'D'. Can you explain this answer?

To answer this question you should know the definitions of tensile, compressive and shear stress.
Tensile stress causes change (increases the length of cylinder) in the length of the object, compressive strength changes the volume of the object (it can be applied from all sides of the object), shear stress is applied parallel to the surface of an object (in case of the cylinder shear stress will be parallel to circular surface) we can apply all the three stresses in case of cylinder hence option D is correct.

Tissue of aorta blood vessel is an example of
  • a)
    state of permanant deformation
  • b)
    perfectly plastic body
  • c)
    perfectly elastic body
  • d)
    elastomer
Correct answer is option 'D'. Can you explain this answer?

Gaurav Kumar answered
Elastomers are popular in vascular engineering applications, as they offer the ability to design implants that match the compliance of native tissue.
Substances like tissue of aorta can be stretched to cause large strain.

If proportional limit is not exceeded, energy per unit volume in stretched wire is
  • a)
    1/2 x stress x strain
  • b)
    stress x strain
  • c)
    stress x strain 2
  • d)
    1/2 stress x strain 2
Correct answer is 'A'. Can you explain this answer?

Suresh Reddy answered
strain energy=1/2×stress × strain Work done by a force on a wire
W =2LAy(ΔL)2/2L
=1/2(yALΔ/L)ΔL
=1/2​(yΔL/L)(ΔL/L)(AL)
=1/2(Stress)(Strain)(Volume)
(Work)/(volume)=1/2(stress)(strain)

In Hooke’s law, the constant of proportionality signifies
  • a)
    modulus of elasticity
  • b)
    modulus of strain
  • c)
    elasticity of wire
  • d)
    modulus of stress
Correct answer is option 'A'. Can you explain this answer?

Introduction:
Hooke's Law is a principle in physics that relates the force applied to a spring or elastic material to the resulting deformation or change in length of the material. It states that the force applied to a spring is directly proportional to the displacement or change in length of the spring.

Explanation:
The constant of proportionality in Hooke's Law is known as the modulus of elasticity or Young's modulus. It is represented by the symbol 'E' and is a measure of the stiffness or rigidity of a material. The modulus of elasticity signifies how much a material will deform when a force is applied to it.

Modulus of Elasticity:
The modulus of elasticity is a material property that describes how it responds to stress. It is defined as the ratio of stress to strain within the elastic limit of the material. In other words, it measures how much stress a material can withstand before it starts to deform permanently.

Modulus of Strain:
The modulus of strain is not a property used in Hooke's Law. Strain is the measure of deformation or change in length of a material, and the modulus of strain is not directly related to the constant of proportionality in Hooke's Law.

Elasticity of Wire:
The elasticity of a wire refers to its ability to return to its original shape after being stretched or deformed. It is related to Hooke's Law as the law describes the linear relationship between the force applied to a wire and the resulting deformation or change in length of the wire.

Modulus of Stress:
The modulus of stress is not a term used in Hooke's Law. Stress is defined as the force applied per unit area of a material, and the modulus of stress is not directly related to the constant of proportionality in Hooke's Law.

Conclusion:
In conclusion, the constant of proportionality in Hooke's Law signifies the modulus of elasticity. It is a measure of the stiffness or rigidity of a material and describes how much a material will deform when a force is applied to it. The modulus of elasticity is a fundamental property used to understand the behavior of elastic materials and is essential in various fields such as engineering and materials science.

A body is said to be perfectly elastic if
  • a)
    it can move freely
  • b)
    it is not effected by external force
  • c)
    it recovers its original shape / size when the deforming force is removed
  • d)
    its surface is perfectly smooth
Correct answer is option 'C'. Can you explain this answer?

Hansa Sharma answered
A body is said to be perfectly elastic when its coefficient of restitution is 1 or we observe total  reformation in the body. That means that whatever hits it doesn't lose any of its kinetic energy or once the body gets totally reformed after a collision.

How does the modulus of elasticity change with temperature?
  • a)
    It does not depend on temperature
  • b)
    It decreases with increase in temperature
  • c)
    It increases with increase in temperature
  • d)
    It sometimes increases, sometimes decreases with increase in temperature
Correct answer is option 'B'. Can you explain this answer?

Pooja Shah answered
As the temperature increases, the inter-atomic distance also increases. So, it results in an increase in the area (stress = force /area). As the area increases stress decreases, this results in a decrease in Young's modulus.

The stress which is set up in the body due to increase in its dimensions is called
  • a)
    volumetric stress
  • b)
    Tangential stress
  • c)
    Normal stress
  • d)
    Tensile stress
Correct answer is option 'D'. Can you explain this answer?

Rahul Bansal answered
Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress.

The area occupied below the stress-strain graph and above strain axis gives the value of
  • a)
    work done in producing extension
  • b)
    energy stored in the material
  • c)
    Restoring force.
  • d)
    energy density of the material
Correct answer is option 'D'. Can you explain this answer?

Jayant Mishra answered
The area under the stress-strain curve represents the mechanical energy per unit volume consumed by the material. This is true in the elastic range of the graph where the energy is reversibly sorted within the material. Area under the stress strain curve depicts the energy absorbed by the material prior to failure.

What type of stress is produced in a body when the deforming force produces sheer strain?
  • a)
    shear stress
  • b)
    Longitudinal stress
  • c)
    Normal stress
  • d)
    Tangential stress
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
Explanation:
When a deforming force is applied to a body in a direction parallel to its surface, it produces a shear strain. Shear strain is the deformation that occurs when one layer of a material slides past another layer. This type of deformation produces shear stress, which is the force that is acting parallel to the surface of the material. Shear stress is calculated as the force per unit area and is expressed in units of pressure, such as pascals (Pa) or pounds per square inch (psi).

volume strain is defined
  • a)
    as the change in volume ΔV
  • b)
    as the ratio of change in volume (ΔV) to the original volume V
  • c)
    as the ratio of change in volume (ΔV) to thrice the original volume V
  • d)
    as the ratio of change in volume (ΔV) to twice the original volume V
Correct answer is option 'B'. Can you explain this answer?

Imk Pathsala answered
Volume Strain Definition


  • Definition: Volume strain is defined as the ratio of change in volume (ΔV) to the original volume V.


Detailed Explanation


  • Volume strain is a measure of how much a material changes in volume under stress.

  • It is calculated by taking the change in volume and dividing it by the original volume of the material.

  • Volume strain is usually expressed as a decimal or a percentage.

  • It is an important concept in physics and engineering, especially in the study of materials and structures.

  • Understanding volume strain is crucial for predicting how materials will behave under different conditions and loads.

Rectangular section is rarely used in beams because
  • a)
    stresses are uniform in a rectangular section
  • b)
    more material in kilos is required
  • c)
    stresses are always plastic in rectangular section
  • d)
    less material in kilos is required
Correct answer is option 'B'. Can you explain this answer?

Anjali Iyer answered
I section is generally used as a beam because of its high section modulus as it's most of the area is situated away from it's neutral axis hence it has high moment of inertia i.e high section modulus i.e high moment carrying capacity which is the major requirement for a good beam section.

Two wires P and Q of same length and material but radii in the ratio 2 : 1 are suspended from a rigid support. Find the ratio of strain produced in the wires when both are under same force.
  • a)
    1:2
  • b)
    4:1
  • c)
    1:4
  • d)
    2:1
Correct answer is option 'C'. Can you explain this answer?

Upasana Bose answered
Using Hooke ‘s Law we get
Stress directly proportional to stress = Load/Area=F/pie*r*r
And rp:rq=2:1
When both the wires are under the same stress,strain produced will be the same.
 
When both the wires are under the same stress,strain produced will be the same.
2.when both the wires are loaded by same weight then
Strain p/strain q=(rq)2/(rp)2

The length of the wire is increased by 1 mm on the application of a given load. In a wire of the same material but of length and radius twice that of the first, on application of the same force, extension produced is
  • a)
    0.25 mm
  • b)
    2 mm
  • c)
    4 mm
  • d)
    0.5 mm
Correct answer is option 'D'. Can you explain this answer?

Shreya Gupta answered
Let F be the load applied on the wire of length L, area of cross-section a; such that the produced extension is I ( = 1 mm ) 
F=Y a l/L.... ( i ) 
Now, when same force F is applied on the wire of same material with length 2L and radius 2 R , let the extension produced be r . 
Then, l' = F(2L) Y ( 4 a ) 
Or, substituting the value of F from ( i ) , we get
I' = 1 / 2 
or, 1' = 1mm/ 2 = 0.5 mm 

An Indian rubber cube of side 10 cm has one side fixed while a tangential force of 1800 N is applied to the opposite side. Find the shear strain produced. Take η = 2 x 106 N/ m2.
  • a)
    0.9
  • b)
    0.009
  • c)
    0.09
  • d)
    9
Correct answer is option 'C'. Can you explain this answer?

Mohit Rajpoot answered
To calculate the shear strain, we use the formula:
shear strain = shear stress / shear modulus.
Shear stress is defined as force/area.
Here, the area is 10 cm × 10 cm = 0.1 m × 0.1 m = 0.01 m².
Therefore, the shear stress is 1800 N / 0.01 m² = 180,000 N/m².
Given the shear modulus (η) is 2 × 10⁶ N/m²,
the shear strain = 180,000 N/m² / 2 × 10⁶ N/m² = 0.09.
Hence, the correct answer is option c) 0.09.

Columns are loaded in
  • a)
    shear
  • b)
    hydraulic stress
  • c)
    tension
  • d)
    compression
Correct answer is option 'D'. Can you explain this answer?

Madhavan Patel answered
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages.

A perfectly rigid body is one
  • a)
    whose shape and size change on application of force
  • b)
    which does not move on application of force
  • c)
    which starts flowing like water on application of force
  • d)
    whose shape and size do not change on application of force
Correct answer is option 'D'. Can you explain this answer?

Arka Bose answered
Explanation:A perfectly rigid body is hypothetical in nature but for some phenomena ( in rotational bodies ) we assume bodies are perfectly rigid i.e. the intermolecular forces are always in equilibrium irrespective of the external forces due to which their shape and size are constant.

When too many people stand on a bridge it collapses, why?
  • a)
    Due to increase in stress
  • b)
    Due to overweight
  • c)
    Due to improper construction
  • d)
    Due to friction
Correct answer is option 'A'. Can you explain this answer?

Sai Mishra answered
Stress is the force per unit area experienced by the body and strength is the ability to withstand the stress. When stress becomes greater than strength, accidents happen.

After prolonged use, springs deform permanently because of
  • a)
    its rigidity
  • b)
    elastic fatigue
  • c)
    elastic after effect
  • d)
    plastic fatigue
Correct answer is option 'B'. Can you explain this answer?

Rohan Singh answered
Springs deform permanently because of elastic fatigueness. The elasticity of the material of spring is lost and it deforms permanently. 

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