Quiz: Mechanical Engineering 25 June 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Thermal

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. A jet engine has
(a) No propeller
(b) Propeller in front
(c) Propeller at back
(d) Propeller on the top

Q2. In a uni-flow engine
(a) Steam enters and exhausts through the same port
(b) Steam enters at one end and exhausts at the center
(c) Steam enters at the center and exhausts at the other end
(d) None of the above

Q3. Specific heat of air increases with increase in
(a) Temperature
(b) Pressure
(c) Both pressure and temperature
(d) Variations of its constituents

Q4. The variables which control the physical properties of a perfect gas are
(a) Pressure exerted by the gas
(b) Volume occupied by the gas
(c) Temperature of the gas
(d) All of the above

Q5. Total emissivity of polished silver surface as compared to black surface is
(a) Same
(b) More or less same
(c) less
(d) Very much lower

Q6. The region between the separated streamline and the boundary surface of the solid body after separation is known as
(a) Drag
(b) Wake
(c) Lift
(d) Boundary layer

Q7. A true one-dimensional flow occurs when
(a) The direction and magnitude of the velocity at all points are identical
(b) The magnitude and direction of the velocity do not change from point to point in the fluid
(c) The velocity of successive fluid particles, at any point is the same at successive periods of time
(d) The fluid particles move in plane or parallel planes and the streamline patterns are identical to each other

Q8. Which of the following hydraulic unit is used to transmit increased or decreased torque to driven-shaft?
(a) Hydraulic torque converter
(b) Hydraulic intensifier
(c) Hydraulic ram
(d) Hydraulic accumulator

Q9. At lower temperature and pressures, the latent heat of vaporization of a refrigerant
(a) increases
(b) decreases
(c) remains same
(d) None of these

Q10. Which of the following will reduce volumetric efficiency of a vertical CI engine?
(a) Inlet valve closing before BDC
(b) Inlet valve closing after BDC
(c) Inlet valve opening before TDC
(d) Exhaust valve closing after TDC

Solutions

S1. Ans.(a)
Sol. A jet engine is a type of reaction engine. It produces thrust by jet propulsion by discharging a fast-moving jet.

S2. Ans.(b)
Sol. In a uni-flow engine, steam enters at one end and exhaust at the center.

S3. Ans.(a)
Sol. Specific heat of air increases with increase in temperature because at elevated temperatures, one or more constituents of air will gain more degrees of freedom, which allows them to store more heat. This, in turn, means that more heat should be supplied for the temperature change.

S4. Ans.(d)
Sol. According to ideal gas equation,
PV=nRT
Here,
P = Pressure exerted by the gas
V = volume occupied by the gas
T = Temperature of the gas
So, physical properties of a perfect or ideal gas are dependent on P, V, T of the gas.

S5. Ans.(d)
Sol. Polished surface emissivity (0.02) is much lower than that of black surface (0.97) at room temperature.

S6. Ans.(b)
Sol. The space or region between separated streamline and boundary surface is known as wake. In the wake, so much dissipation of energy takes place and it is an undesirable phenomenon due to the same reason.

S7. Ans.(a)
Sol. When the direction and magnitude of the velocity at all points are identical, then it is known as true one-dimensional flow.

S8. Ans.(a)
Sol. Torque converter is a fluid coupling in which three or more rotors are used, one of which can be checked so that output torque is augmented and output speed diminished and vice versa.

S9. Ans.(a)
Sol. As the temperature and pressure of refrigerant decreases then the refrigerant effect and latent heat of vaporization increase in a vapour compression refrigeration cycle.

S10. Ans.(a)
Sol. If inlet valve closes before BDC in CI engine then its volumetric efficiency decreases because of the less time available for charge(air) admission into the cylinder. For high volumetric efficiency, inlet valve should close after BDC.

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