Mock Test: SSC JE (ME)- 7 - Mechanical Engineering MCQ

The moment diagram for a cantilever beam that carries a uniformly distributed load is typically represented by a parabolic shape.

• The shape arises because the moment varies along the length of the beam.
• At the fixed support, the moment is at its maximum, gradually decreasing towards the free end.
• This relationship is due to the nature of the load being uniformly distributed across the beam.
• Understanding this diagram is essential for analysing beam behaviour under load.

The moment diagram for a cantilever beam with a concentrated load at the end will be shaped like a triangle.

This is because:

• The moment varies linearly along the length of the beam.
• At the fixed support, the moment is at its maximum.
• As you move towards the free end, the moment decreases to zero.

Therefore, the correct representation of the moment diagram is a triangle.

Turbines can trip due to various operational issues.

• An increase in inlet pressure can lead to a trip. This condition might indicate a blockage or malfunction that requires immediate attention.

• If the speed of the turbine rises uncontrollably, it poses a risk of damage and can trigger a safety mechanism to shut down the system.

• When the turbine blades are eroded due to wear, it can compromise performance and safety, necessitating a trip to prevent further damage.

• A significant increase in mass flow might indicate operational anomalies, which can also lead to a turbine trip for safety reasons.

In summary, a turbine is most likely to trip when there is an uncontrolled speed increase.

Diesel is in principle easier to refine than gasoline, however it contains more pollutants that must be extracted before it can reach the same levels of emissions as petrol. Per litre, diesel contains more energy than petrol and the vehicle’s engine combustion process is more efficient, adding up to higher fuel efficiency and lower CO2 emissions when using diesel.

The rollers in a cycle chain experience various types of stress, which can significantly affect their performance and durability. Understanding these stresses is crucial for maintaining the efficiency of the chain.

• Compressive Stress: This occurs when forces push the rollers together, compressing them. While present, it is not the primary concern for roller chains.
• Tensile Stress: This type of stress happens when the rollers are pulled apart. It can lead to elongation and wear, but it is also not the main issue in this context.
• Bending Stress: Bending occurs when the chain experiences forces that cause it to curve. This stress can lead to deformation of the rollers.
• Fatigue Stress: The most critical stress for roller chains. It occurs due to repeated loading and unloading cycles, leading to the gradual weakening of the material over time. This can result in cracks and eventual failure.

In summary, while rollers are subjected to multiple stresses, fatigue is the most significant factor affecting their longevity and effectiveness.

Two sheets of the same material but different thickness can be butt welded by:

• Adjusting the current: Modifying the electrical current can help achieve a strong weld between the sheets.

• Changing the duration: The time the current is applied is crucial; longer durations can enhance the weld quality.

• Applying pressure: The amount of pressure used during welding affects the bond strength.

• Altering electrode size: Adjusting the size of one electrode can optimise the weld process for different thicknesses.

• Thickness of the plate: Thicker plates require more current for effective welding.

• Length of the welded portion: A longer weld may need increased current for uniform heating.

• Voltage across the arc: The voltage affects the arc stability, which in turn influences current settings.

• Diameter of the electrode: Larger electrodes demand higher current levels for proper melting.

Each of these factors plays a crucial role in achieving a successful weld. Understanding their impact helps welders adjust settings for optimal performance.

Neutral flame is characterised by the following:

• It has two distinct zones: the inner and outer cone.

• The inner cone is typically light blue and indicates a complete combustion.

• The outer cone is pale blue and shows a stable flame.

• This flame is used for various welding applications due to its balanced nature.

The neutral flame is essential for processes that require a stable and controlled heat source.

Sands are classified based on several key factors:

• Source of origin: This refers to where the sand is obtained, such as riverbeds, beaches, or deserts.

• Strength: The ability of the sand grains to withstand pressure and stress.

• Permeability: This indicates how easily water can flow through the sand, which affects its use in construction.

• Clay content and grain size: The amount of clay mixed with the sand and the size of the grains can influence its properties.

The time taken for a metal casting to solidify is influenced by its properties.

• The volume of the metal in the casting plays a significant role.
• A larger volume generally leads to a longer solidification time.
• The surface area of the casting also affects this process.
• A greater surface area allows for better heat dissipation, potentially reducing the solidification time.

In summary, the relationship between volume and surface area is crucial:

• More volume = longer solidification time.
• More surface area = shorter solidification time.

Understanding these factors is essential for optimising the casting process and ensuring quality outcomes in metalworking.

As the size of castings increases, it is often better to use increasingly

• Fine grain: This option offers better detail and precision, making it suitable for smaller castings.

• Medium grain: A balanced choice that provides a good mix of strength and detail, ideal for medium-sized castings.

• Coarse grain: Best used for larger castings, as it allows for easier flow of materials and reduces the risk of defects.

In summary, for larger castings, coarse grain is generally preferred due to:

• Improved material flow during casting.
• Reduced likelihood of defects.
• Better structural integrity in large components.

The usual ratio of forward and return strokes in a shaper is

• The forward stroke is the cutting stroke.
• The return stroke is the non-cutting stroke.
• The typical ratio used is 2:1.
• This means that for every two forward strokes, there is one return stroke.
• This ratio maximises efficiency in the shaping process.

Using this ratio helps in:

• Reducing production time.
• Improving overall machine performance.
• Ensuring a smoother operation of the shaper.

A long column fails due to various factors.

• Crushing: This occurs when the column is unable to withstand the compressive forces acting on it.
• Tension: While columns are primarily designed to handle compression, excessive tension can lead to failure.
• Shearing: This refers to the failure that happens when forces cause the material to slide past itself, weakening the structure.
• Buckling: This is a critical mode of failure for long columns, where they deform under compressive loads, leading to instability.

Among these, buckling is particularly significant for long columns, as it can occur even at loads lower than the material's compressive strength. Understanding these failure modes is essential for proper design and safety considerations in structural engineering.

E = Stress / Strain = WL / ΔL A
For a tapering rod,
A = π d1 d2 / 4
ΔL = 4WL / π d1 d2 E
For a uniform cross section with diameter d,
A = π d² / 4
 ΔL = 4WL / π d² E

The bars have the same length l and are subjected to the same axial pull W. Then for the same extension ΔL
4WL / π d1 d2 E = 4WL / π d² E
1/ d1d2 = 1/ d^{2
so d =} 

- Spring Work Formula: The work done to stretch a spring is given by the formula  W=1/2​k(x_f²​−x_i²​), where k is the spring constant,  x_f is the final displacement, and x_i is the initial displacement.

- Given:
- Spring constant, k = 1000 N/m
- Initial stretch, x_i= 0.1 m, (10 cm)
- Final stretch, x_f = 0.2 m (20 cm)

- Calculating Work:
W=1/2(1000)((0.2)²−(0.1)²)
W=500(0.04−0.01)
W=500⋅0.03=15 J
- Conclusion: The work required is 15J which is equivalent to 15 Nm, which corresponds to option D.

In planetary motion, the parameter that remains constant is total angular momentum.

Total angular momentum is crucial in understanding how planets and other celestial bodies move in space. Here are some key points:

• Total angular momentum is conserved in a closed system, meaning it does not change over time.
• This conservation applies to all bodies in motion, including planets orbiting stars.
• While other factors like angular velocity and linear velocity may vary, total angular momentum remains constant unless an external force acts on the system.
• This principle helps astronomers predict the motion of planets and other celestial entities.

Thus, understanding the conservation of total angular momentum is essential for studying planetary motion.

The moment of inertia is a fundamental concept in physics that describes how difficult it is to change the rotation of an object. Importantly, this measure does not rely on certain factors:

• Angular velocity: The speed at which an object rotates does not affect its moment of inertia.
• Mass: While the mass of the body is crucial for other calculations, the moment of inertia itself is independent of the total mass.
• Distribution of mass: Although the arrangement of mass within the object is essential, the moment of inertia remains unaffected by how the mass is distributed.
• Axis of rotation: The specific line about which an object rotates does not change the moment of inertia.

In summary, the moment of inertia is determined by the shape and distribution of mass but is not influenced by the factors mentioned above.

When a body falls freely under gravitational force, it experiences a unique condition.

• The body is influenced solely by gravity.
• During free fall, the body does not experience any air resistance.
• As a result, it appears to have no weight in the context of its motion.
• This state leads to a sensation of weightlessness for the object.

Thus, while the body's mass remains constant, the effects of gravity make it seem as though it has no weight during free fall.

Francis, Kaplan, and propeller turbines are types of turbines used in various engineering applications.

These turbines are classified as reaction turbines. Here are some key points about them:

• Reaction turbines operate on the principle of both pressure and kinetic energy.
• They convert the energy of water into mechanical energy as water flows through the turbine.
• Common examples include the Francis and Kaplan turbines.
• These turbines are designed to work efficiently at varying water flow conditions.

Understanding the classification of turbines is essential for selecting the appropriate type for specific applications, such as hydroelectric power generation.

Reaction turbines are specifically designed for various water flow conditions. They are most effective in the following scenarios:

• Lower head and higher flows: These turbines excel in situations where water is abundant and the pressure is lower.
• They convert the energy in flowing water into mechanical energy efficiently, making them suitable for specific applications.

In summary, reaction turbines are optimal for:

• Lower head conditions
• Higher flow rates

In a static fluid:

• The resistance to shear stress is minimal.

• The fluid pressure is zero.

• Linear deformation remains small.

• Only normal stresses can exist.

Chain drive is the preferred choice for applications requiring a constant velocity ratio and a positive drive between the driver and driven shafts, especially when there is a large centre distance. Here are the key reasons for its suitability:

• Efficiency: Chain drives transmit power efficiently, with minimal energy loss.
• Durability: Chains are robust and can withstand high loads, making them ideal for heavy machinery.
• Minimal Slippage: Unlike belts, chain drives do not slip, ensuring consistent performance.
• Adjustable Centre Distance: They can easily accommodate varying distances between shafts, providing flexibility in design.

In contrast, other drive types may not perform as well under similar conditions:

• Gear drives: While they provide a constant velocity ratio, they require precise alignment and can be more complex.
• Flat belt drives: These can experience slippage, especially under heavy loads.
• V-belt drives: Similar to flat belts, they may also slip and are less effective over large distances.

Therefore, for applications that demand reliability and efficiency over large distances, chain drives are the optimal choice.

Mitre gears are designed to connect shafts that are at an angle to each other, typically at 90 degrees. They are characterised by their conical shape and are often used in applications where space is limited.

Spiral bevel gears also connect shafts at an angle and provide smoother operation due to their helical teeth. They are known for their efficiency and ability to handle higher loads, making them suitable for various mechanical systems.

Hypoid gears allow for non-intersecting shafts and enable offset axes. They provide a high level of torque transmission and are commonly used in automotive rear axles.

Zerol gears are similar to spiral bevel gears but have a zero angle between the axes. They also create a smooth operation and are used in applications requiring high precision.

• Mitre Gears: Ideal for 90-degree shafts.
• Spiral Bevel Gears: Provide smooth operation and higher load capacity.
• Hypoid Gears: Allow for non-intersecting shafts with high torque.
• Zerol Gears: Enable high precision with a zero angle between axes.

In a governor, if the equilibrium speed is constant for all radii of rotation of balls, the governor is said to be:

• The term isochronous refers to a system that maintains a constant speed regardless of changes in the radius of rotation.
• This means that the governor's performance remains stable throughout different operating conditions.
• In an isochronous governor, the speed does not vary, which is essential for applications requiring precise control.
• This characteristic allows for consistent functionality in various mechanical systems.

Centrifugal tension in belts can have significant effects on their performance. Here are the key points to consider:

• Increased Tension: Centrifugal tension can lead to higher overall tension in the belt.
• Power Transmission: This increased tension may reduce the amount of power transmitted effectively.
• Operational Impact: While some tension is necessary for operation, excessive centrifugal tension can be detrimental.
• Not a Myth: It is a real phenomenon, not just a theoretical concept.

In summary, while centrifugal tension maintains some belt tension, it can be harmful to the efficiency of power transmission.