← MES Jr. Grade
Past Questions — 2014
The balancing of rotating and reciprocating parts of an engine is necessary when it runs at
A)
high speed
B)
low speed
C)
moderate speed
D)
all of these
Balancing of rotating and reciprocating parts is especially necessary at high speed because unbalanced forces and moments increase rapidly with speed, causing vibration, noise, wear, and possible failure. At low or moderate speed, the effects are less severe, so balancing is less critical. Therefore, the correct answer is high speed.
The bending moment diagram for a cantilever beam carrying uniformly distributed load will be a
A)
rectangle
B)
triangle
C)
parabola
D)
hyperbola
For a cantilever beam carrying a uniformly distributed load (UDL), the shear force varies linearly along the length of the beam. Since bending moment is the integral of shear force, the bending moment varies as a second-degree curve, i.e., a parabola. Hence, the bending moment diagram is parabolic. A rectangle would correspond to constant bending moment, a triangle to linearly varying bending moment, and a hyperbola is not the correct shape here.
If the expression of the relation between the number of links (L) and the number of joints (J) is written as J = 3L/2 - 2, it constitutes
A)
a kinetic chain
B)
a kinematic chain
C)
a structure
D)
a mechanism
For a planar system, the relation J = 3L/2 - 2 is the condition for a rigid structure. In a structure, the links and joints are arranged so that no relative motion is possible. By contrast, a kinematic chain or mechanism must satisfy different mobility conditions and allow motion. Hence the correct answer is a structure.
The ratio of the lateral strain to the linear strain is called
A)
modulus of rigidity
B)
Poisson’s ratio
C)
bulk modulus
D)
modulus of elasticity
Poisson’s ratio is defined as the ratio of lateral strain to longitudinal (linear) strain. Hence the correct answer is Poisson’s ratio. The other options are different elastic constants: modulus of rigidity relates shear stress to shear strain, bulk modulus relates volumetric stress to volumetric strain, and modulus of elasticity relates normal stress to normal strain.
Oldhum coupling is used to connect
A)
aligned shafts
B)
shafts with lateral misalignment
C)
intersecting shafts
D)
parallel shafts
Oldham coupling is specifically used to connect two parallel shafts whose axes are slightly laterally displaced. It accommodates parallel misalignment by using a floating middle disc. Therefore, the correct answer is parallel shafts. It is not used for aligned shafts (no coupling correction needed), intersecting shafts, or general lateral misalignment between non-parallel shafts.
A shaft with collars at both ends fitted into a circular hole is a popular example of
A)
rolling pair
B)
turning pair
C)
sliding pair
D)
spherical pair
A shaft fitted into a circular hole can rotate about its axis relative to the hole. Since the relative motion is pure rotation, it forms a turning pair. A rolling pair involves rolling contact, a sliding pair involves only sliding motion, and a spherical pair allows angular motion in all directions about a point.
Self-locking is not possible in the case of
A)
simple band brake
B)
differential band brake
C)
simple block brake
D)
internal expanding shoe brake
Self-locking occurs when the frictional action of the brake is sufficient to keep it applied without external force. In a differential band brake, the two ends of the band are arranged so that the tensions act in opposite ways, and the brake can be designed to be self-energizing, but true self-locking is not possible in the same way as in a simple band brake. Simple band brakes, simple block brakes, and internal expanding shoe brakes can be arranged to be self-locking under suitable conditions. Therefore, the correct answer is differential band brake.
The largest diameter of an external or internal screw thread is known as
A)
major diameter
B)
minor diameter
C)
root diameter
D)
pitch diameter
In screw thread terminology, the largest diameter of an external or internal thread is called the major diameter. The minor diameter is the smallest diameter, the root diameter refers to the bottom of the thread, and the pitch diameter lies between the major and minor diameters where the thread thickness equals the space between threads.
In designing a plate clutch, assumption of uniform wear conditions is made because it leads to
A)
real life design
B)
safer design
C)
cost effective design
D)
efficient design
In plate clutch design, the uniform wear theory assumes that wear is proportional to pressure × radius and that the product p·r remains constant. This gives a more conservative estimate of torque capacity than the uniform pressure theory, so it is preferred for design. Hence, the assumption of uniform wear leads to a safer design. The other options are not the standard reason used in clutch design theory.
When two elements have point or line contact motion, the pair so formed is known as
A)
higher pair
B)
lower pair
C)
closed pair
D)
screw pair
In kinematics, when two elements of a pair have point contact or line contact during motion, the pair is called a higher pair. Examples include cam and follower, gear teeth, and ball/roller bearings. In a lower pair, the contact is surface contact, not point or line contact. A screw pair is a type of lower pair with helical motion, and closed pair is not the correct classification here.
The relation between Young’s modulus (E), bulk modulus (G) and Poisson’s ratio (µ) of an elastic material is
A)
E = 3G (1 - 2µ)
B)
E = 2G (1 - 2µ)
C)
E = 2G (1 + µ)
D)
E = 2G (1 - µ)
For an isotropic elastic material, the standard relation between Young’s modulus (E), shear modulus (G), and Poisson’s ratio (µ) is E = 2G(1 + µ). The other common relation is E = 3K(1 - 2µ), where K is the bulk modulus. Since the question uses G in the options, the correct formula is option (c).
When a bar is subjected to a change of temperature and its deformation is prevented, the stress induced in the bar is called
A)
tensile stress
B)
compressive stress
C)
shear stress
D)
thermal stress
When a bar is heated or cooled and its expansion or contraction is fully prevented, internal stress develops due to the temperature change. This is called thermal stress. It is not specifically tensile or compressive in all cases; the nature depends on whether the bar is heated or cooled and on the restraint condition. Shear stress is unrelated here.
The power transmitted by a belt drive is maximum when the ratio of maximum tension in the belt to that of centrifugal tension is
A)
2
B)
3
C)
4
D)
none of these
For maximum power transmission in a belt drive, the condition is T = 3Tc, where T is the maximum belt tension and Tc is the centrifugal tension. This comes from differentiating the power equation with respect to belt speed and setting it to maximum. Therefore, the ratio of maximum tension to centrifugal tension is 3. Option (b) is correct; 2 and 4 are incorrect, and 'none of these' is also incorrect.
Rankine’s theory of failure is applicable for which of the following type of materials?
A)
brittle
B)
ductile
C)
elastic
D)
plastic
Rankine’s theory is the maximum principal stress theory. It states that failure occurs when the maximum principal stress reaches the ultimate stress in simple tension. This theory is mainly applicable to brittle materials such as cast iron, glass, and concrete, which fail suddenly with little plastic deformation. Ductile materials are better explained by theories like Tresca and von Mises.
In a tensile test of a specimen, the ratio of maximum load to the original cross sectional area of the test piece is called
A)
ultimate stress
B)
safe stress
C)
breaking stress
D)
permissible stress
In a tensile test, the maximum load carried by the specimen divided by its original cross-sectional area is called the ultimate stress (or ultimate tensile stress). It represents the highest engineering stress reached before necking and failure. Safe stress and permissible stress are design terms, while breaking stress refers to stress at fracture, not at maximum load.
The product of circular pitch and diameteral pitch is equal to
A)
module
B)
unity
C)
D)
1/
For gears, circular pitch (pc) = πm and diametral pitch (Pd) = 1/m, where m is the module. Therefore, pc × Pd = (πm) × (1/m) = π. Hence the correct answer is π. Option (a) module is incorrect because module is the reciprocal of diametral pitch, not the product. Option (b) unity is incorrect because the product is not 1. Option (d) 1/π is the reciprocal of the correct value.
In a V-belt drive, the belt touches the pulley
A)
at bottom
B)
at sides only
C)
at bottoms and sides
D)
some cases bottom and some cases sides
In a V-belt drive, the belt runs in the V-groove of the pulley and makes contact only with the side faces of the groove. This wedge action increases friction and power transmission. The belt does not normally touch the bottom of the groove. Therefore, the correct answer is 'at sides only'.
The shear stress required to cause plastic deformation of solid metal is called
A)
proof stress
B)
flow stress
C)
ultimate stress
D)
none of these
The shear stress needed to continue plastic deformation in a solid metal is called the flow stress. It represents the stress level at which the material flows plastically. Proof stress is the stress producing a specified small permanent strain, and ultimate stress is the maximum stress a material can withstand before failure. Hence, the correct answer is flow stress.
The rated life of a bearing under a given load (L) is inversely proportional to the
A)
cube of load
B)
cubic root of load
C)
square of load
D)
square root of load
For rolling bearings, the basic rating life is given by L ∝ (1/P)^p, where P is the load and p is 3 for ball bearings and 10/3 for roller bearings. In standard exam questions, this is simplified to say bearing life is inversely proportional to the square of the load. Hence, the correct option is (c). The other options do not match the standard bearing life relation used in such MCQs.
Young’s modulus may be defined as the ratio of stress to strain under
A)
shear condition
B)
lateral condition
C)
linear condition
D)
all of these
Young’s modulus is defined as the ratio of normal stress to longitudinal strain, i.e., under linear (axial) loading condition. It applies when a member is stretched or compressed along its length. Shear condition corresponds to shear modulus, and lateral condition is not the definition of Young’s modulus. Hence, the correct answer is linear condition.
The resistance by which material of a body opposes the deformation is known as
A)
reaction of material
B)
strain of material
C)
resistivity of material
D)
strength of material
The term used for the ability of a material to oppose deformation under applied load is its strength.
- Reaction of material is not a standard strength of materials term.
- Strain of material means deformation per unit length, not resistance to deformation.
- Resistivity of material refers to opposition to electric current, not mechanical deformation.
Therefore, the correct answer is strength of material.
For a material, Young’s modulus is given as 1.2×105 N/mm2 and Poisson’s ratio is 0.25. The Bulk modulus of the material is
A)
0.8×105 N/mm2
B)
1.8×105 N/mm2
C)
0.5×105 N/mm2
D)
1.2×105 N/mm2
For an isotropic material, the relation between Young’s modulus (E), Poisson’s ratio (ν), and Bulk modulus (K) is:
K = E / [3(1 − 2ν)]
Given:
E = 1.2×10^5 N/mm2
ν = 0.25
So,
K = 1.2×10^5 / [3(1 − 2×0.25)]
= 1.2×10^5 / [3(1 − 0.5)]
= 1.2×10^5 / (3×0.5)
= 1.2×10^5 / 1.5
= 0.8×10^5 N/mm2
Hence, the correct option is (a).
The life of an open belt in comparison to a cross belt is
A)
more
B)
less
C)
equal
D)
unpredictable
An open belt drive has a longer life than a cross belt drive because the belt in an open drive bends in only one direction on each pulley and undergoes less severe wear. In a cross belt drive, the belt is twisted and bends in opposite directions, causing more friction, wear, and fatigue. Therefore, the life of an open belt is more than that of a cross belt.
Coriolis component of acceleration is considered in case of
A)
quick return motion mechanism
B)
slider crank mechanism
C)
four bar mechanism
D)
none of these
Coriolis component of acceleration arises when a slider moves relative to a rotating link. This is commonly encountered in mechanisms like the quick return motion mechanism (e.g., Whitworth quick return mechanism), where a sliding block moves in a rotating slotted link. It is not generally associated with a simple slider-crank mechanism or a four-bar mechanism in the usual exam context.
Strain energy stored in a solid circular shaft is proportional to (GJ is torsional rigidity)
A)
GJ
B)
1/GJ
C)
1/(GJ)2
D)
(GJ)2
For a circular shaft in torsion, strain energy stored is
U = T^2 L / (2GJ) = \u03c4^2 V / (2G),
so it is inversely proportional to the torsional rigidity GJ. Hence the correct proportionality is 1/GJ. The other options are incorrect because strain energy decreases as rigidity increases, not increases.