← MES Jr. Grade
Past Questions — 2014
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.
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.
At node of the shaft, the vibrations are
A)
minimum
B)
maximum
C)
zero
D)
any value between minimum and maximum
In vibration theory, a node is a point on a vibrating shaft where displacement is always zero. Hence, at the node of the shaft, the vibrations are zero. The other options are incorrect because maximum vibration occurs at an antinode, not at a node.
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 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.
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.
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.
A beam is loaded as cantilever. If the load at the free end is increased, the failure will occur
A)
at the point of the load
B)
at the middle of the beam
C)
at the fixed end of the beam
D)
at any location of the beam
In a cantilever beam with a load at the free end, the bending moment is maximum at the fixed support and zero at the free end. Since failure in bending occurs where the bending stress is highest, the beam will fail at the fixed end. The other options are incorrect because the load point has no maximum moment, the middle is not the critical section, and failure does not occur at any arbitrary location.
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.
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.
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.
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.
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 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.
Which one of the following is a dead weight governor?
A)
Watt governor
B)
Hartnell governor
C)
Porter governor
D)
Hartung governor
A dead weight governor uses the weight of the balls and sleeve to provide the controlling force. The Porter governor is a dead weight governor. Watt governor is also a dead weight governor in the basic classification, but in standard exam terminology, the Porter governor is the specific dead weight governor among the given options. Hartnell governor is a spring-loaded governor, and Hartung governor is not a dead weight governor.
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.
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'.
A kinematic chain is called a mechanism, if the number of fixed links is
A)
at most one
B)
at least one
C)
more than one
D)
none of these
A kinematic chain becomes a mechanism when one of its links is fixed, so that the relative motion of the remaining links is constrained and useful motion is obtained. Therefore, the number of fixed links must be at least one. If no link is fixed, it remains only a kinematic chain, not a mechanism.
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).
Rankine’s formula for determining the load carrying capacity of a column is valid for
A)
long column only
B)
short column only
C)
columns with hinged ends only
D)
all columns
Rankine’s formula is an empirical formula that combines crushing failure for short columns and buckling failure for long columns. Because it accounts for both extremes, it is used for all columns over a practical range of slenderness ratios. Hence, the correct answer is all columns. The other options are incorrect because it is not limited to only long columns, only short columns, or only hinged-end columns.
Theory of machine which deals with the inertia force due to combined effect of the mass and motion of the various links of the machines is known as
A)
kinetics
B)
kinematics
C)
dynamics
D)
statics
Theory of machines that deals with the inertia forces caused by the combined effect of mass and motion of machine links is called kinetics. Kinematics studies motion without considering forces, dynamics is the broader study of forces and motion, and statics deals with bodies at rest or in equilibrium.
In design analysis, factor of safety is defined as the ratio between material strength and
A)
yield strength
B)
ultimate strength
C)
maximum load
D)
allowable strength
Factor of safety is defined as the ratio of material strength to the working or allowable stress/strength. In design, it indicates how much stronger a system is than the minimum required. Hence, the correct relation is strength divided by allowable strength. Option (a) yield strength and (b) ultimate strength are material properties, not the denominator in the definition. Option (c) maximum load is not the standard definition of factor of safety.
A fluid in which resistance of deformation is independent of the shear stress is known as
A)
Bingham plastic fluid
B)
Pseudo plastic fluid
C)
Dilatent fluid
D)
Newtonian fluid
A Newtonian fluid has a linear relationship between shear stress and rate of shear strain, so its viscosity remains constant and the resistance to deformation is independent of the applied shear stress. In contrast, Bingham plastic fluids require a yield stress, pseudo-plastic fluids are shear-thinning, and dilatant fluids are shear-thickening.