Quiz: Mechanical Engineering 18 May 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. Which one of the following statements is correct?
(a) A machine which violates Clausius statement will violate the first law of thermodynamics
(b) A machine which violates Kelvin-Plank statement will violate the first law of thermodynamics
(c) A machine which violates the second law of thermodynamics will violate the first law of thermodynamics
(d) A machine which violates Kelvin-Plank statement will violate the Clausius statement

Q2. The conditioned air supplied to the room must have the capacity to take up
(a) Room sensible heat load only
(b) Room latent heat load only
(c) Both room sensible heat load and room latent heat load
(d) Neither room sensible heat load nor room latent heat load

Q3. Consider the following statements:
1. In model testing, the same fluid must be used in prototype and also the model
2. Models should be smaller than prototype for geometric similarity
3. Geometrically similar boundaries do not necessarily imply kinematically homogeneous flows
4. Existence of geometric similarity does not imply dynamic similarity
Which of the above statements are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 3 and 4 only
(d) 1 and 4 only

Q4. The discharge through a converging-diverging nozzle reaches its maximum value when the flow becomes
(a) Sonic at the exit
(b) Sonic at the throat
(c) Supersonic at the throat
(d) Subsonic at the throat

Q5. ‘Shockless entry’ of water in hydraulic turbines is of much significance from the standpoint of
(a) Hydraulic efficiency
(b) Mechanical efficiency
(c) Both hydraulic efficiency and mechanical efficiency
(d) Neither hydraulic efficiency nor mechanical efficiency

Q6. In solving a lumped parameter problem, which one of the following pair of non-dimensional numbers is used?
(a) Grashoff number and Biot number
(b) Prandtl number and Nusselt number
(c) Biot number and Fourier number
(d) Fourier number and Reynolds number

Q7. Which one of the following key types is pressed against the shaft for power transmission by friction between the key and the shaft?
(a) Feather key
(b) Square key
(c) Flat key
(d) Saddle key

Q8. The difference between member of a truss and of a beam is:
(a) The members of a truss take their loads along their length whereas a beam takes loads at right angles to its length
(b) The member of the truss takes load lateral to its length whereas the beam along the length
(c) The member of the truss can be made of C.I whereas the beam is of structural steel only
(d) The member of the truss can have a circular cross-section whereas the beam can have any cross-section

Q9. For an Oldham coupling used between two shafts, which among the following statements are correct?
I. Torsional load is transferred along shaft axis.
II. A velocity ratio of 1:2 between shafts is obtained without using gears
III. Bending load is transferred transverse to shaft axis.
IV. Rotation is transferred along shaft axis.
(a) I and II
(b) I and IV
(c) II and III
(d) II and IV

Q10. The maximum theoretical work obtainable, when a system interacts to equilibrium with a reference environment, is called
(a) Entropy
(b) Enthalpy
(c) Exergy
(d) Rothalpy

SOLUTIONS

S1. Ans(d)
Sol. A machine which violates kelvin-plank statement will violate the Clausius statement because
Kelvin-plank states that it is impossible to construct a device which operates in a cycle with single fixed temperature heat reservoir while Clausius states that it is impossible to construct a device which transfer heat from a lower temperature reservoir to a high temperature reservoir without any kind of work input. These two statements are complimentary to each other.

S2. Ans(c)
Sol. The conditioned air supplied to the room must have the capacity to take up Both room sensible heat and latent heat loads.

S3. Ans(c)
Sol. following observations can be made-
(a) Existence of geometric similarity does not imply dynamic similarity.
(b) Geometrically similar boundaries do not necessarily imply kinematically homogeneous flows.

S4. Ans(b)
Sol. The discharge through a converging-diverging nozzle reaches its maximum value when the flow becomes Sonic at the throat for which Mach number value is 1.

S5. Ans(a)
Sol. ‘Shockless entry’ of water in hydraulic turbines is of much significance from the standpoint of Hydraulic efficiency.
The hydraulic efficiency of hydraulic turbine is very much affected by shock less entry. Shock less entry in turbine ensure that the power loss in the turbine is less.

S6. Ans(c)
Sol. In solving a lumped parameter problem, pair of non-dimensional number such as Biot number and Fourier number is used.
Significance of Biot Number-
(a) Biot Number tells us whether lumped heat analysis is applicable or not.
If Bi<0.1 only then lumped heat analysis is applicable
(b) As it is the ratio of conductive resistance to convective resistance, it signifies low conductive resistance and large convective resistance.
Significance of Fourier Number-
(a) It signifies degree of penetration of heating or cooling effect.
(b) It is a measure of heat conducted through a body relative to heat stored.

S7. Ans(d)
Sol. saddle key is used for power transmission by friction between the key and the shaft.
(a) saddle key – saddle key is the key which is fit into the keyway of the hub only and no keyway in the shaft. It is likely to slip round under the shaft under load.
(b) feather key – feather key is the parallel key which is faster to one part (hub/shaft) with the help of the screws.
(c) square key – square key is the key having square cross-section.
(d) flat key – flat key is a taper key having provision in the hub only and will be floated on the shaft and the shaft is hold by mean of friction.

S8. Ans(b)
Sol. The difference between member of a truss and of a beam is the member of the truss takes load lateral to its length whereas the beam along the length.
Truss- A truss is a structure that consists of members organised into connected triangles so that the overall assembly behaves as a single object. Trusses are most commonly used in bridges, roofs and towers. A truss is made up of a web of triangles joined together to enable the even distribution of weight and the handling of changing tension and compression without bending or shearing. The triangle is geometrically stable when compared to a four (or more) -sided shape which requires that the corner joints are fixed to prevent shearing.
Beam- A beam is a structural element that primarily resists loads applied laterally to the beam’s axis. Its mode of deflection is primarily by bending. The loads applied to the beam result in reaction forces at the beam’s support points. The total effect of all the forces acting on the beam is to produce shear forces and bending moments within the beam, that in turn induce internal stresses, strains and deflections of the beam. Beams are characterized by their manner of support, profile (shape of cross-section), equilibrium conditions, length, and their material.

S9. Ans(b)
Sol. Oldham’s coupling is used to transmit power between two shafts having small angular misalignment. There is no bending load or reduction/increase of speed criterion. Hence only I and IV statements are correct.

S10. Ans(c)
Sol. As per the definition of the Exergy (or) Available Energy, we know that the maximum portion of energy which could be converted into useful work by ideal processes which reduce the system to dead state is known as Exergy.

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