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All questions of Solids for ACT Exam

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.

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.

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,

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?

Rahul Bansal answered
Since mud or putty have no gross tendency to regain their previous shape & they get permanently deformed, they are close to ideal plastics.

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?

Lavanya Menon answered
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.

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)

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.

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

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.

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

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.

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.

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.

Compute the fractional change in volume of a glass slab, when subjected to a hydraulic pressure of 10 atm. Bulk modulus of glass 37 GPa.
  • a)
    0.0027
  • b)
    0.0030
  • c)
    0.0024
  • d)
    0.0022
Correct answer is option 'A'. Can you explain this answer?

Given data:
Bulk modulus of glass = 37 GPa
Hydraulic pressure = 10 atm

Formula used:
Bulk modulus of elasticity (K) = (pressure * volume)/(volume change)

Calculation:
Let initial volume of the glass slab be V₀ and let the change in volume be ΔV.
Bulk modulus of elasticity (K) = (pressure * volume)/(volume change)

⇒ K = (10 atm * V₀)/(ΔV)

⇒ ΔV/V₀ = (10 atm * V₀)/K

⇒ ΔV/V₀ = (10 atm * V₀)/(37 × 10⁹ N/m²)

⇒ ΔV/V₀ = 2.7 × 10⁻⁶

Hence, the fractional change in volume of a glass slab, when subjected to a hydraulic pressure of 10 atm, is 0.0027. Therefore, option A is the correct answer.

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.

Elasticity is the property of a body, by virtue of which
  • a)
    it remains in original size and shape when the force is applied
  • b)
    it changes size and shape when the force is applied and stays in that shape when applied force is removed
  • c)
    it tends to regain its original size and shape when the applied force is removed
  • d)
    it is distorted or stretches without the application of force
Correct answer is option 'C'. Can you explain this answer?

Lavanya Menon answered
Explanation:When external force is applied on the solid bodies, the solid bodies get deformed. The atoms or molecules are displaced from their equilibrium positions causing a change in the interatomic ( or intermolicular ) distances. When the deforming foce is removed, the interatomic forces tend to drive them back to their original postions. Thus the body regains its original shape and size.

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.

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

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.

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.

A piece of copper having a rectangular cross-section of 15.2 mm × 19.1 mm is pulled in tension with 44,500 N force, producing only elastic deformation. Calculate the resulting strain? Take Young's modulus of copper as 42 × 10
9
Pa
  • a)
    3.65 × 10-8
  • b)
    3.65 × 10-3
  • c)
    3.65 × 10-9
  • d)
    3.65 × 10-2
Correct answer is option 'B'. Can you explain this answer?

Anjana Sharma answered
Given Data,
Length of the piece of copper = l = 19.1 mm = 19.1 × 10-3m
Breadth of the piece of copper = b = 15.2 mm = 15.2× 10-3m
Tension force applied on the piece of cooper, F = 44500N
Area of rectangular cross section of copper piece,
Area = l× b
⇒ Area = (19.1 × 10-3m) × (15.2× 10-3m)
⇒ Area = 2.9 × 10-4 m2
Modulus of elasticity of copper from standard list, η = 42× 109 N/m2
By definition, Modulus of elasticity, η = stress/strain

⇒ Strain = F/Aη

⇒ Strain = 3.65 × 10-3
Hence, the resulting strain is 3.65 × 10-3

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.

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.

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. 

Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion: The stretching of a coil is determined by its shear modulus.
Reason: Shear modulus change only shape of a body keeping its dimensions unchanged.
  • a)
    If both assertion and reason are true and the reason is the correct explanation of the assertion.
  • b)
    If both assertion and reason are true but reason is not the correct explanation of the assertion.
  • c)
    If assertion is true but reason is false.
  • d)
    If the assertion and reason both are false.
Correct answer is option 'A'. Can you explain this answer?

Sahana Joshi answered
Assertion: The stretching of a coil is determined by its shear modulus.
Reason: Shear modulus changes only the shape of a body while keeping its dimensions unchanged.

Explanation:
To understand the given assertion and reason, let's first define the terms involved:

- Stretching: It refers to the extension or elongation of a body when a force is applied to it.
- Coil: It is a helical structure usually made of a flexible material like metal wire, which can be stretched or compressed.
- Shear modulus: It is a measure of the rigidity of a material and represents its resistance to shearing forces. It quantifies the elasticity of a material in response to shear stress.

Now, let's analyze the assertion and reason:

Assertion: The stretching of a coil is determined by its shear modulus.
This means that the shear modulus of a coil material influences how much the coil can be stretched when a force is applied to it. In other words, the shear modulus determines the elasticity and flexibility of the coil material, which directly affects its stretching behavior.

Reason: Shear modulus changes only the shape of a body while keeping its dimensions unchanged.
This reason suggests that when a shear force is applied to a body, it deforms by changing its shape but not its dimensions. In the case of a coil, the shear modulus determines how much the coil can be deformed or stretched while maintaining its original dimensions.

Explanation of Correct Answer:
The correct answer is option 'A': If both the assertion and reason are true and the reason is the correct explanation of the assertion.

The reason provided in the given statement aligns with the assertion. The shear modulus of a coil material indeed determines its stretching behavior, as it reflects the material's elasticity and flexibility. Additionally, the reason explains that the shear modulus only changes the shape of a body while keeping its dimensions constant, which is relevant to the stretching behavior of a coil.

Therefore, the assertion and reason are both true, and the reason correctly explains the assertion.

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