Quiz: Mechanical Engineering
Exam: UPSSSC JE
Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes
Q1. A closed thermodynamic system is one in which
(a) there is no energy or mass transfer across the boundary
(b) there is no mass transfer, but energy transfer exists
(c) there is no energy transfer, but mass transfer exists
(d) both energy and mass transfer take place across the boundary, but the mass transfer is controlled by valves
Q2. Which one of the following represents the condensation of a mixture of saturated liquid and saturated vapour on the enthalpy-entropy diagram?
(a) A horizontal line
(b) an inclined line of constant slope
(c) A vertical line
(d) A curved line
Q3. Consider the following statements:
1. The increase in metacentric height
2. Increases stability
3. Decreases stability
4. Increases comfort for passengers in a ship
5. Decreases comfort for passengers in a ship
Which of the above statements are correct?
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4
Q4. Which one of the following is measured by a rotameter?
(a) Velocity of fluids
(b) Discharge of fluids
(c) Viscosity of fluids
(d) Rotational speed of solid shafts
Q5. When a liquid flow through a tube with sub-cooled or saturated boiling, what is the process known?
(a) Pool boiling
(b) Bulk boiling
(c) Convection boiling
(d) Forced convection boiling
Q6. The turbomachine used to circulate refrigerant in large refrigeration plant is
(a) A centrifugal compressor
(b) A radial turbine
(c) An axial compressor
(d) An axial turbine
Q7. Air at 35°C DBT and 25°C dew point temperature passes through the water shower whose temperature is maintained at 20°C. What is the process involved?
(a) cooling and humidification
(b) sensible cooling
(c) cooling and dehumidification
(d) heating and humidification
Q8. In an internally pressurized thick cylinder, the hoop stress
1. Remains constant but the radial stress varies parabolically
2. Varies parabolically but the radial stress remains constant
Which of the above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Q9. Which of the following are associated with Ackerman steering mechanism used in automobiles?
1. Has both sliding and turning pairs
2. Less friction and hence long life
3. Mechanically correct in all positions
4. Mechanically not accurate except in three positions
5. Has only turning pairs
6. Controls movement of two front wheels
(a) 2, 4, 5 and 6
(b) 1, 2, 3 and 6
(c) 2, 3, 5 and 6
(d) 1, 2, 3 and 5
Q10. In a tensile test on mild steel specimen, the breaking stress as compared to ultimate tensile stress is
(d) more/less depending on composition
Sol. A closed system consists of fixed amount of mass and no mass can cross its boundary but energy in the form of heat and work can cross the boundary.
Sol. For Mollier diagram, condensation takes place at constant pressure which is along vertically inclined.
S3. Ans (b)
Sol. Time period of oscillations is inversely proportional to meta centric height. Thus, more the GM less will be time period, and body regains its position in less time. So more stable.
Sol. Rotameter and elbow meter measure discharge through pips
S5. Ans (b)
Sol. Pool Boiling: In this case the liquid above the hot surface is essentially stagnant and its motion near the surface is due to free convection.
Forced Convection Boiling: This refers to a situation where the fluid motion is induced by external means. This type of boiling occurs in water tube boilers involving forced convection.
Sub-Cooled or Local Boiling: In this case the liquid temperature is below the saturation temperature and bubbles are formed in the vicinity of heat surface.
Saturated Boiling: Here, the liquid temperature exceeds the saturation temperature.
S6. Ans (a)
Sol. Large amount of vapour refrigerant at low pressure is required to handle in large refrigerant plant. Also unlike reciprocating compressor, centrifugal compressor are steady-flow device hence subjected to less vibration and noise.
Sol. As the temperature of water shower is less than dew point temperature hence, water vapour starts condensing. Thus, process involved is cooling and dehumidification.
Sol. For thick cylinder
1. Variations of hoop stress and radial stress are parabolic across the cylinder wall.
2. at the inner edge, the stresses are maximum.
3. the value of ‘permissible or Maximum Hoop stress’ is to be considered on the inner edge,
4. the maximum shear stress (σmax) and Hoop, longitudinal and radial strains (εh,εl,εr) are calculated as in thin cylinder but separately for inner and outer edges.
Sol. the following things are associated with Ackerman steering mechanism used in automobiles.
1. Less friction and hence long life
2. Mechanically correct in all positions
3. Mechanically not accurate except in three positions
4. Has only turning pairs
5. Controls movement of two front wheels
S10. Ans (b)
Sol. Ultimate stress is the maximum value of stress. It is the point at which the size (cross section area) decreases and a neck is formed, and breaking stress is the stress at which the material actually breaks down.
The value of ultimate stress is always more than the breaking stress as formation of neck (permanent deformation) requires more stress than to actually break.