← MES Jr. Grade
Past Questions
Convert [2 1 -1 -1] from four-index system to three-index system.
A)
[2 1 0]
B)
[3 0 1]
C)
[1 -1 -1]
D)
[1 -2 1]
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is '[3 0 1]' (Option B).
In hot working of metals, the working temperature is
A)
below the recrystallisation temperature
B)
above the recrystallisation temperature
C)
equal to the melting point of the metal
D)
150°
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'below the recrystallisation temperature' (Option A).
In sheet metal work, the cutting force on the tool can be reduced by
A)
grinding the cutting edges sharp
B)
increasing the hardness of tool
C)
providing shear angle on tool
D)
increasing the hardness of die
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'grinding the cutting edges sharp' (Option A).
Which of the following point defects is non-stoichiometric in nature?
A)
Schottky defect
B)
Metal excess defect
C)
Interstitial defect
D)
Impurity defect
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Metal excess defect' (Option B).
In an ideal inventory control system, the economic lot size for a part is 1000. If the annual demand for the part is doubled, the new economic lot size required will be
A)
500
B)
2000
C)
1000/ 2
D)
1000 √2
Based on established principles in the relevant subject area, the correct and most appropriate choice is '500' (Option A).
Consider the following statements with respect to PERT : 1. It consists of activities with uncertain time phases. 2. This is evolved from Gantt Chart. 3. Total slack along the critical path is not zero. 4. There can be more than one critical path in PERT network. 5. It is similar to electrical network. Which of the statement given above are correct?
A)
1, 2 and 5
B)
1, 3, and 5
C)
2, 4, and 5
D)
1, 2 and 4
Based on established principles in the relevant subject area, the correct and most appropriate choice is '1, 2 and 4' (Option D).
Delta iron occurs in this temperature range
A)
1400°C to 1530°C
B)
723 to 910°C
C)
910 to 1400°C
D)
400 to 723°C
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is '400 to 723°C' (Option D).
Brass is an alloy of
A)
Copper and zinc
B)
Tin and zinc
C)
Copper and tin
D)
Copper and Al
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Copper and zinc' (Option A).
Arc stability is better with
A)
AC welding
B)
DC welding
C)
Both AC and DC welding
D)
Specially designed wave forms
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'AC welding' (Option A).
Pearlite phase in steel is made up of
A)
alternate layers of martensite and cementite
B)
alternate layers of ferrite and cementite
C)
alternate layers of ferrite and martensite
D)
alternate layers of bainite and cementite
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'alternate layers of ferrite and cementite' (Option B).
Gantt chart gives the information about
A)
the utilisation of man power
B)
the number of jobs to be completed
C)
the quantity of material flow into the process
D)
the production schedule
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'the production schedule' (Option D).
Which one of the following is not equilibrium heat treatment
A)
Austenetising
B)
Annealing
C)
Normalizing
D)
Precipitation
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Austenetising' (Option A).
Delphi method of forecasting is applicable
A)
when previous data from the market are available
B)
when a study about a product already in the market is required
C)
when a new product is launched in the market
D)
the market is highly competitive
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'when a new product is launched in the market' (Option C).
‘Shadow price’ is the term used in linear programming to denote
A)
Optimum cost assigned to the variable
B)
Value assigned to one unit of capacity
C)
Maximum cost/unit
D)
Minimum cost/unit
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Minimum cost/unit' (Option D).
The cam follower extensively used in aircraft engines is
A)
Knife edge follower
B)
Flat faced follower
C)
Spherical faced follower
D)
Roller follower
In aircraft engines, particularly in the valve mechanisms of internal combustion engines, flat-faced followers are extensively used. The primary reasons are: 1. Reduction of Stress: A flat face distributes the contact load over a larger area compared to a knife-edge or roller follower, reducing the contact stress (Hertzian stress) on the cam surface. 2. Stability at High Speeds: At the very high rotational speeds typical of aircraft engines, roller followers can suffer from 'skidding' or 'sliding' if the roller cannot keep up with the cam profile, leading to rapid wear. Flat-faced followers eliminate the risk of roller skidding. 3. Compactness: They allow for a more compact design in the cylinder head.
Comparison with other options:
- Knife edge followers (a) are theoretical and suffer from extreme wear due to high contact stress; they are never used in actual engines.
- Spherical faced followers (c) are used to reduce stress compared to knife-edge but are less efficient than flat-faced followers for the specific high-load, high-speed requirements of aircraft valves.
- Roller followers (d) are common in automotive engines to reduce friction, but in high-performance aircraft engines, the risk of roller skidding and the added mass/complexity often make the flat-faced follower the preferred choice for specific valve train designs.
In a reinforced concrete section, shear stress distribution is diagrammatically
A)
Wholly Parabolic
B)
Wholly Rectangular
C)
Parabolic above N-A and Rectangular below N-A
D)
Rectangular above N-A and Parabolic below N-A
In a reinforced concrete (RC) beam, the shear stress distribution differs from that of a homogeneous beam due to the presence of longitudinal reinforcement.
1. Above the Neutral Axis (N-A): The concrete is the primary material resisting the compressive forces. The shear stress distribution follows the standard formula τ = (VQ/Ib), which results in a parabolic distribution, reaching its maximum at the neutral axis.
2. Below the Neutral Axis (N-A): In the tension zone, the concrete is assumed to be cracked and cannot carry tension. Therefore, the tensile force is carried entirely by the steel reinforcement. Because the steel bars have a very small area compared to the concrete but carry the full tensile load, the shear stress is transferred abruptly to the reinforcement. This results in a distribution that is effectively rectangular (or nearly constant) across the depth of the tension zone as the shear is transferred to the steel.
Therefore, the distribution is parabolic in the compression zone (above N-A) and rectangular in the tension zone (below N-A).
The surface of the gear tooth below the pitch surface is called
A)
addendum portion
B)
dendendum portion
C)
flank
D)
face
In gear terminology, the tooth profile is divided into two main regions relative to the pitch circle:
1. The portion of the tooth surface above the pitch circle is called the 'Face'.
2. The portion of the tooth surface below the pitch circle is called the 'Flank'.
Evaluating the options:
- Option (a) 'addendum portion' refers to the radial distance from the pitch circle to the top of the tooth, not the surface itself.
- Option (b) 'dedendum portion' (misspelled as dendendum) refers to the radial distance from the pitch circle to the bottom of the tooth space.
- Option (c) 'flank' is the correct term for the surface below the pitch surface.
- Option (d) 'face' is the surface above the pitch surface.
A thin cylindrical shell of diameter (d), length (l) is subjected to an internal pressure (p). The circumferential stress in the shell is
A)
2pd/t
B)
4pd/t
C)
6pd/t
D)
8pd/t
Based on established principles in the relevant subject area, the correct and most appropriate choice is '4pd/t' (Option B).
The type of stresses developed in the key is/are
A)
both shear and bearing stresses
B)
bearing stress alone
C)
shear stress alone
D)
shearing, bearing and bending stresses
A key is a machine element used to connect a rotating machine element (like a gear or pulley) to a shaft to prevent relative rotation between them. When torque is transmitted, the key is subjected to several types of stresses:
1. **Shearing Stress**: The torque creates a force that tends to shear (cut) the key across the plane where the shaft and the hub meet. This is the primary failure mode for most keys.
2. **Bearing (Crushing) Stress**: The sides of the key are pressed against the keyway of the shaft and the hub. This compressive stress is known as bearing or crushing stress.
3. **Bending Stress**: In many practical scenarios, the key does not fit perfectly or the pressure is not uniformly distributed across the entire depth. This causes the key to act like a cantilever beam, inducing bending stresses. This is particularly significant in 'sunk keys'.
While basic textbook problems often simplify calculations to only shear and bearing, a comprehensive engineering analysis of a key's failure must account for all three: shearing, bearing, and bending. Therefore, option (d) is the most complete and accurate answer.
A cotter joint is used to transmit
A)
axial tensile load only
B)
axial compressive load only
C)
combined axial and twisting loads
D)
axial tensile or compressive loads
A cotter joint is a temporary fastening used to connect two co-axial rods. Its primary function is to transmit axial loads.
1. **Axial Tensile Load:** When the rods are pulled apart, the cotter acts as a wedge that prevents the rods from separating, thus transmitting the tensile force.
2. **Axial Compressive Load:** When the rods are pushed together, the shoulders of the socket and spigot members resist the force, transmitting the compressive load.
Why other options are incorrect:
- Option (a) and (b) are incomplete because the joint is capable of handling both types of axial loads, not just one.
- Option (c) is incorrect because a cotter joint is not designed to transmit twisting (torsional) loads; for torsion, a keyed shaft or a splined joint would be used. The cotter joint is specifically designed for linear (axial) movement/force.
If a composite bar is cooled, then the nature of stress in the part with high coefficient of thermal expansion will be
A)
tensile
B)
zero
C)
compressive
D)
none of these
In a composite bar consisting of two different materials bonded together, the total deformation must be the same for both materials to maintain the integrity of the bond.
1. **Thermal Expansion/Contraction**: The change in length due to temperature change is given by $\Delta L = L \alpha \Delta T$, where $\alpha$ is the coefficient of thermal expansion.
2. **Cooling Effect**: When the composite bar is cooled ($\Delta T$ is negative), both materials want to contract. The material with the higher coefficient of thermal expansion ($\alpha_{high}$) will attempt to contract more than the material with the lower coefficient ($\alpha_{low}$).
3. **Internal Constraint**: Because they are bonded, the material with the lower $\alpha$ prevents the material with the higher $\alpha$ from contracting fully.
4. **Resulting Stress**: Since the material with the higher $\alpha$ is 'held back' from its natural tendency to shrink, it is effectively being pulled or stretched relative to its desired cooled state. This results in **tensile stress** in the part with the higher coefficient of thermal expansion and **compressive stress** in the part with the lower coefficient of thermal expansion to maintain equilibrium.
The value of Poisson’s ratio for steel varies from
A)
0.20 to 0.25
B)
0.25 to 0.35
C)
0.35 to 0.40
D)
0.40 to 0.55
Poisson's ratio (ν) is the ratio of lateral strain to longitudinal strain when a material is stretched or compressed. For most structural metals, this value typically falls between 0.25 and 0.35. Specifically for steel, the value is generally accepted to be around 0.27 to 0.30.
- Option (a) 0.20 to 0.25: This is generally too low for standard structural steel.
- Option (b) 0.25 to 0.35: This range accurately encompasses the standard value for steel (approx. 0.3).
- Option (c) 0.35 to 0.40: This range is more typical for materials like aluminum or certain plastics.
- Option (d) 0.40 to 0.55: Values approaching 0.5 are characteristic of perfectly incompressible materials like rubber. Steel is far more rigid and has a lower ratio.
A screw is said to be a self-locking screw, if its efficiency is
A)
Less than 50%
B)
More than 50%
C)
Equal to 50%
D)
None of these
A screw is considered 'self-locking' if it does not rotate backward under the influence of the axial load it is supporting. Mathematically, this occurs when the friction angle (φ) is greater than the helix angle (α).
1. Efficiency (η) of a screw is given by the formula: η = tan(α) / tan(α + φ).
2. For a screw to be self-locking, the condition is φ > α.
3. If φ = α, the efficiency is exactly 50% (assuming no collar friction).
4. If φ > α (self-locking condition), the denominator tan(α + φ) increases significantly relative to the numerator tan(α), resulting in an efficiency of less than 50%.
5. Conversely, if the efficiency is greater than 50%, the screw is 'overhauling,' meaning it will rotate back under the load.
Therefore, a self-locking screw must have an efficiency of less than 50%.
When a solid shaft is subjected to torsion, the shear stress induced in the shaft at it centre is
A)
zero
B)
minimum
C)
maximum
D)
average
The distribution of shear stress in a solid circular shaft subjected to torsion is governed by the torsion formula: τ = (T × r) / J, where τ is the shear stress, T is the applied torque, r is the radial distance from the center of the shaft, and J is the polar moment of inertia. According to this linear relationship, the shear stress is directly proportional to the distance from the center (axis) of the shaft. At the center of the shaft, the radius r = 0. Substituting this into the formula: τ = (T × 0) / J = 0. Therefore, the shear stress at the center is zero. Conversely, the shear stress reaches its maximum value at the outer surface of the shaft where r is equal to the radius of the shaft.
In order to facilitate starting of locomotive in any position, the cranks of a locomotive with two cylinders, are placed at
A)
45° to each other
B)
90° to each other
C)
120° to each other
D)
180° to each other
In a two-cylinder locomotive, the 'crank angle' refers to the angular displacement between the cranks of the two cylinders. If the cranks were placed at 180° (opposite to each other), the locomotive would encounter a 'dead center' position where both pistons are at the ends of their strokes simultaneously. In such a case, if the locomotive stopped exactly at this point, it would be impossible to start it using steam power alone because the force would act directly along the axis of the connecting rod, producing no torque on the axle. By placing the cranks at 90° to each other, it is ensured that when one cylinder is at its dead center (zero torque), the other cylinder is at its point of maximum leverage (maximum torque). This ensures that the locomotive can be started from any position, regardless of where the pistons are in their stroke.