Mechanical Engineering Thermodynamics

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Q1. The index of compression ‘n’ tends to reach ratio of specific heats ‘y’ when

(A) Flow is uniform and steady
(B) Process is isentropic
(C) Process is isothermal
(D) Process is isentropic and specific heat does not change with temperature

Answer: (D) Process is isentropic and specific heat does not change with temperature

Q2. The efficiency of Diesel cycle increases with

(A) Increase in cut-off
(B) Constant cut-off
(C) Decrease in cut-off
(D) None of these

Answer: (C) Decrease in cut-off

Q3. Otto cycle consists of following four processes

(A) Two isothermal and two isentropic
(B) Two isentropic and two constant volumes
(C) Two isentropic, one constant volume and one constant pressure
(D) Two isentropic and two constant pressures

Answer: (B) Two isentropic and two constant volumes

Q4. Which of the following cycles is not a reversible cycle?

(A) Carnot
(B) Ericsson
(C) Stirling
(D) None of the above

Answer: (D) None of the above

Q5. A cycle consisting of _ and two isothermal processes is known as Stirling cycle.

(A) Two isentropic
(B) One constant pressure, one constant volume
(C) Two constant volumes
(D) Two constant pressures

Answer:(C) Two constant volumes

Q6. A closed system is one in which

(A) Mass does not cross boundaries of the system, though energy may do so
(B) Mass crosses the boundary but not the energy
(C) Neither mass nor energy crosses the boundaries of the system
(D) Both energy and mass cross the boundaries of the system

Answer: (A) Mass does not cross boundaries of the system, though energy may do so

Q7. Intensive property of a system is one whose value

(A) Depends on the mass of the system, like volume
(B) Does not depend on the mass of the system, like temperature, pressure, etc.
(C) Is not dependent on the path followed but on the state
(D) Is dependent on the path followed and not on the state

Answer: (B) Does not depend on the mass of the system, like temperature, pressure, etc.

Q8. Work done in a free expansion process is

(A) +ve
(B) -ve
(C) Zero
(D) Maximum

Answer: (C) Zero

Q9. According to Kelvin-Planck’s statement of second law of thermodynamics,

(A) It is possible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work
(B) It is impossible to construct a device which operates in a cyclic process and produces no effect other than the transfer of heat from a cold body to a hot body
(C) It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work
(D) None of the above

Answer: Option C

Q10. One watt is equal to

(A) 1 Nm/s
(B) 1 N/m
(C) 1 Nm/hr
(D) 1 kNm/hr

Answer: (A) 1 Nm/s

Q11. Which of the following processes is irreversible process?

(A) Isothermal
(B) Adiabatic
(C) Throttling
(D) All of the above

Answer: (C) Throttling

Q12. The specific heat at constant volume is

(A) The amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume
(B) The amount of heat required to raise the temperature of unit mass of gas through one degree, at constant pressure
(C) The amount of heat required to raise the temperature of 1 kg of water through one degree
(D) Any one of the above

Answer: (A) The amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume

Q13. Which of the following is the correct statement of the second law of thermodynamics?

(A) There is a definite amount of mechanical energy, which can be obtained from a given quantity of heat energy
(B) It is impossible to transfer heat from a body at a lower temperature to a higher temperature, without the aid of an external source
(C) It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work
(D) All of the above

Answer: (D) All of the above

Q14. Barometric pressure is equal to

(A) 760 mm Hg
(B) Zero mm Hg
(C) 735.6 mm Hg
(D) 1 mm Hg

Answer: (A) 760 mm Hg

Q15. Kinetic energy of the molecules in terms of absolute temperature (T) is proportional to

(A) T
(B) J
(C) J²
(D) Vr

Answer: (A) T

Q16. Change in enthalpy of a system is the heat supplied at

(A) Constant pressure
(B) Constant temperature
(C) Constant volume
(D) Constant entropy

Answer: (A) Constant pressure

Q17. The amount of heat required to raise the temperature of the unit mass of gas through one degree at constant volume, is called

(A) Kilo Joule
(B) Specific heat at constant volume
(C) Specific heat at constant pressure
(D) None of these

Answer: (B) Specific heat at constant volume

Q18. The efficiency of a Carnot engine depends on

(A) Working substance
(B) Design of engine
(C) Size of engine
(D) Temperatures of source and sink

Answer: (D) Temperatures of source and sink

Q19. The cycle in which heat is supplied at constant volume and rejected at constant pressure is known as

(A) Dual combustion cycle
(B) Diesel cycle
(C) Atkinson cycle
(D) Rankine cycle

Answer: (C) Atkinson cycle

Q20. A tri-atomic molecule consists of __ atoms.

(A) Three
(B) One
(C) Two
(D) Four

Answer: (A) Three

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