Quiz: Mechanical Engineering 19 May 2020

Quiz: Mechanical Engineering
Exam: ISRO Technical Assistant
Topic: Miscellaneous

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 thermodynamic processes approximates the steaming of food in a pressure cooker?
(a) isenthalpic
(b) isobaric
(c) isochoric
(d) isothermal

Q3. Specific speed of a fluid machine
(a) refers to the speed of a machine of unit dimensions
(b) is a type-number representative of its performance
(c) is specific to the particular machine
(d) depends only upon the head under which the machine operates

Q4. The component of torque converter that allows torque multiplication is
(a) Turbine
(b) Impeller
(c) Stator
(d) Freewheel

Q5. Increase in entropy of a system represents
(a) Increase in availability of energy
(b) Increase in temperature
(c) Decrease in pressure
(d) Degradation of energy

Q6. Priming is necessary in
(a) Centrifugal pumps to lift water from a greater depth
(b) centrifugal pumps to remove air in the suction pipe and casing
(c) Hydraulic turbine to remove air in the turbine casing
(d) Hydraulic turbine to increase the speed of turbine and to generate more power

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. Piston compression rings are made of which one of the following?
(a) Cast iron
(b) Bronze
(c) Aluminium
(d) White metal

Q9. The Klein’s method of construction for reciprocating engine mechanism
(a) is based on acceleration diagram
(b) is a simplified from of instantaneous centre method
(c) utilizes a quadrilateral similar to the diagram of mechanism for reciprocating engine
(d) enables determination of Coriolis component

Q10. In resistance welding, voltage used for heating is
(a) 1 V
(b) 10 V
(c) 100 V
(d) 500 V

Solutions

S1. Ans.(b)
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.

S2. Ans.(c)
Sol. Volume of pressure cooker is always constant hence it is isochoric process.

S3. Ans (b)
Sol. Specific speed is of a fluid machine is a type number representative of its performance.
In order to compare the performance of different pumps, it is necessary to have some term which will be common to all the centrifugal pump the term ordinarily used for this purpose is the specific speed. This is a type characteristic and can be used to predict the behaviour of one pump based on tests of similar, but different sized pumps.
The specific speed is a characteristic of pumps which can be used as basis for comparison of the performance of different pump.

S4. Ans (c)
Sol. A hydraulic torque converter consists of series of fixed guide vanes which are provided between turbine runner and pump impeller. The liquid exerts a torque on the driven unit through these stationary guide vanes as it flows from pump to turbine runner.

S5. Ans (d)
Sol. Entropy is the measure of degree of Randomness. Increase in entropy of a system represents degradation of energy.

S6. Ans.(b)
Sol. filling the pump casing and the suction pipe with the liquid before it is started is known as priming. Unless the centrifugal pump is primed, it will not start as there is no centrifugal head impressed on the liquid. Positive displacement type reciprocating or rotary pump do not need priming because the air, if any, in the cylinder or casing is driven out by the piston or vanes.

S7. Ans.(c)
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.

S8. Ans.(a)
Sol. Since grey cast iron has properties of self-lubrication and damping of small Vibration they are widely used for machine base, engine frames, drainage pipes, elevator and industrial furnace counter weights, pump housings cylinder and piston rings of IC engines, flywheel etc.

S9. Ans (c)
Sol. In Klein’s Construction, the velocity and the acceleration diagrams are made on the configuration diagram itself. The line that represents the crank in the configuration diagram also represents the velocity and acceleration of its moving end in the velocity and acceleration diagram.

S10. Ans (b)
Sol. Resistance welding processes are pressure welding processes in which heavy current is passed for short time through the area of interface of metals to be joined. These processes differ from other welding processes in the respect that no fluxes are used, and filler metal rarely used. All resistance welding operations are automatic and, therefore, all process variables are presents and maintained constant. Heat is generated in localized area which is enough to heat the metal to sufficient temperature, so that the parts can be joined with the application of pressure. Pressure is applied through the electrodes.
The process employs currents of the order of few KA, voltages range from 2 to 12 volts and times vary from few milliseconds to few seconds.

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