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All questions of Mechanical Properties of Solids for NEET Exam

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.

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.

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.

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

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

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.

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.

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).

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

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?

Ameya Unni answered
Understanding Volume Strain
Volume strain is an important concept in mechanics and materials science that describes how a material deforms when subjected to external forces.
Definition of Volume Strain
- Volume strain is defined specifically as the ratio of the change in volume (ΔV) to the original volume (V0) of a material.
- Mathematically, it can be expressed as: Volume Strain = ΔV / V0.
Why Option B is Correct
- Change in Volume (ΔV): This represents the difference between the final volume after deformation and the initial volume before deformation.
- Original Volume (V0): This is the volume of the material before any external forces have been applied.
- Ratio Significance: By taking the ratio of the change in volume to the original volume, we obtain a dimensionless quantity that allows for comparison across different materials and conditions.
Other Options Explained
- Option A (Change in Volume V): This does not provide a comparative metric and lacks the necessary context of the original volume.
- Option C (Thrice the Original Volume): This is an arbitrary scaling that does not conform to the standard definition of volume strain.
- Option D (Twice the Original Volume): Similar to Option C, this does not reflect the true relationship defined in mechanics.
Conclusion
In conclusion, volume strain is fundamentally about understanding how a material's volume changes relative to its original volume, which is effectively captured by Option B. This definition is crucial for engineers and scientists to assess material behavior under stress.

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.

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 

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. 

Elastomers are materials
  • a)
    which can be stretched without corresponding stress
  • b)
    which cannot be stretched to cause large strains
  • c)
    which cannot be stretched to beyond elastic limit
  • d)
    which can be stretched to cause large strains
Correct answer is option 'D'. Can you explain this answer?

Rajeev Saxena answered
An elastomer is a polymer with viscoelasticity (i. e., both viscosity and elasticity) and very weak intermolecular forces, and generally low Young's modulus and high failure strain compared with other materials. Elastomer rubber compounds are made from five to ten ingredients, each ingredient playing a specific role. Polymer is the main component, and determines heat and chemical resistance, as well as low- temperature performance. Reinforcing filler is used, typically carbon black, for strength properties.

The final point on the stress strain graph is called
  • a)
    Fracture point
  • b)
    yield point
  • c)
    Elastic point
  • d)
    Proportional limit
Correct answer is option 'A'. Can you explain this answer?

Alok Mehta answered
This part of stress strain curve is called hardening region.When the load reaches a maximum value, the engineering stress at this point is called the tensile strength or ultimate tensile strength of the material.

Dimensional formula of stress is same as that of
  • a)
    pressure
  • b)
    impulse
  • c)
    force
  • d)
    strain
Correct answer is option 'A'. Can you explain this answer?

Mira Sharma answered
This means stress is newtons per square meter, or N/m^2. However, stress has its own SI unit, called the pascal. 1 pascal (symbol Pa) is equal to 1 N/m^2. In Imperial units, stress is measured in pound-force per square inch, which is often shortened to "psi". The dimension of stress is the same as that of pressure.

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