Thermodynamics

First law of Thermodynamics | GATE MCQs (solved)

GATE ME solved Questions on First Law of Thermodynamics


Question #1

Steam at an initial enthalpy of 100 kJ/kg and inlet velocity of 100 m/s, enters an insulated horizontal nozzle. It leaves the nozzle at 200 m/s. The exit enthalpy (in kJ/kg) is __________

[GATE 2016 Set 2, 2 marks]


Question #2

Work is done on an adiabatic system due to which its velocity changes from 10 m/s to 20 m/s, elevation increases by 20 m and temperature increases by 1 K. The mass of the system is 10 kg, Cv = 100 J/(kg.K) and gravitational acceleration is 10 m/s2. If there is no change in any other component of the energy of the system, the magnitude of total work done (in kJ) on the system is _______

[GATE 2015 Set 2, 2 marks]


Question #3

A well-insulated rigid container of volume 1 m3 contains 1.0 kg of an ideal gas [Cp = 1000 J/(kg.K) and Cv = 800 J/(kg.K)] at a pressure of 105 Pa. A stirrer is rotated at constant rpm in the container for 1000 rotations and the applied torque is 100 N-m. The final temperature of the gas (in K) is

[GATE 2015 Set 1, 2 marks]

(A) 500.0
(B) 773.0
(C) 785.4
(D) 1285.4



Question #4

Specific enthalpy and velocity of steam at an exit of steam turbine, running under steady state, are as given below:

 Specific enthalpy(kJ/kg) Velocity(m/s)
Inlet steam condition 3250 180
Outlet steam condition 2360 5

The rate of heat loss from the turbine per kg of steam flow rate is 5 kW. neglecting changes in potential energy of steam, the power developed in kW by the steam turbine per kg of steam flow rate is

[GATE 2013, 2 marks]

(a)901.2

(b)911.2

(c)17072.5

(d)17082.5


Common data Question (#5 and #6)

Air enters an adiabatic nozzle at 300 kPa, 500 K with a velocity of 10 m/s. It leaves the nozzle at 100 kPa with a velocity of 180 m/s. The inlet area is 80 cm2. The specific heat of air Cp is 1008 J/kg.K.

Question #5

The exit temperature of the air is

(A) 516 K

(B) 532 K

(C) 484 K

(D) 468 K

[GATE 2012, 2 Marks]

Question #6

The exit area of the nozzle in cm2 is

(A) 90.1

(B) 56.3

(C) 4.4

(D) 12.9

[GATE 2012, 2 Marks]


Common data Question (#7 and #8)

The temperature and pressure of air in a large reservoir are 400 K and 3 bar respectively. A converging-diverging nozzle of exit area 0.005 mis fitted to the wall of the reservoir as shown in the figure. The static pressure of air at the exit section of isentropic flow through the nozzle is 50 kPa.The characteristic gas constant and the ratio of specific heats of air are 0.287kJ/kgK and 1.4 respectively

GATE 2011 thermodynamics question

Question #7

The density of air in kg/mat the nozzle exit is

(A) 0.560

(B) 0.600

(C) 0727

(D) 0.800

[GATE 2011, 2 marks]

Question #8

The mass flow rate of air through the nozzle in kg/s is

(A) 1.30

(B) 1.77

(C) 1.85

(D) 2.06

[GATE 2011, 2 marks]


Question #9

A balloon containing an ideal gas is initially kept in an evacuated and insulated room. The balloon ruptures and the gas fills up the entire room. Which of the following statements is TRUE at the end of the above process.

(A) The internal energy of the gas decreases from its initial value, but the enthalpy remains same

(B)  The internal energy of the gas increases from its initial value, but the enthalpy remains same

(C) Both internal energy and enthalpy of the gas remain constant

(D) Both internal energy and enthalpy of the gas increase

[GATE 2008, 2 marks]


Question #10

A rigid, insulated tank is initially evacuated. The tank is connected with a supply line through which air (assumed to ideal gas with constant specific heats) passes at 1 Mpa, 350 oC. A valve connected with the supply line is opened and the tank is charged with air until the final temperature inside the tank reaches 1 MPa.The final temperature inside the tank.

GATE 2008 THERMODYNAMICS QUESTION

(A)is greater than 350oC

(B) is less than 350 oC

(C) is equal to 350 oC

(D) may be greater than less than, or equal to 350oC, depending on the volume of the tank

[GATE 2008, 2 marks]

Ask your doubts in the comment section below

Practice other topics from Thermodynamics:

Basics of thermodynamics

Heat and work

Second law of thermodynamics

2 Comments

  • Reply
    Anonymous
    October 16, 2018 at 9:04 pm

    cannot understand the solution of problem 2

    • Reply
      admin
      October 16, 2018 at 10:20 pm

      The solution is updated. hope you will understand it now

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