Thermodynamics PYQs Set 3 (PDF)

Set 3 of 16 · Questions 61-90 of 459

In the print window choose “Save as PDF”. The file prints without a web address or date line.

Mere Teacher · Previous Year Questions NEET Physics · Thermodynamics · Set 3 (Q61-90)
Scan or visit mereteacher.com for free PYQ practice, timed CBT tests, step-by-step solutions and BroBot AI. Answers and solutions are free with a sign-up.
61. $A bowl filled with very hot soup cools from 98 °C to 86 °C in 2 minutes when the room temperature is 22 °C. How long it will take to cool from75°C to 69°C?$ (1) $2 minutes$ (2) $1.4 minutes$ (3) $0.5 minute$ (4) $1 minute$ 62. $The efficiency of a Carnot's engine, working between steam point and ice point, will be:$ (1) $26.81%$ (2) $37.81%$ (3) $47.81%$ (4) $57.81%$ 63. $The amount of heat needed to heat 200 grams of ice at - 10^{\circ} C to convert it into water at 30^{\circ} C is Specific heat capacity of ice = 2100 J kg^{- 1} K^{- 1} Specific heat capacity of water = 4186 J kg^{- 1} K^{- 1} Latent heat of fusion of ice = 3.35 \times 10^{5} J kg^{- 1}$ (1) $96316 J$ (2) $67000 J$ (3) $92116 J$ (4) $71200 T$ 64. $At constant volume temperature is increased then$ (1) $collision on walls will be less$ (2) $number of collisions per unit time will increase$ (3) $collisions will be in straight lines$ (4) $collisions will not change$ 65. $If α is the coefficient of performance of a refrigerator and ' Q_{1}' is heat released to the hot reservoir, then the heat extracted from the cold reservoir ' Q_{2}' is$ (1) $\frac{α Q _{1}}{α - 1}$ (2) $\frac{α - 1}{α} Q_{1}$ (3) $\frac{α Q _{1}}{1 + α}$ (4) $\frac{1 + α}{α} Q_{1}$ 66. $A heat engine is involved with exchange of heat of 1915 J, - 40 J, + 125 J and - QJ, during one cycle achieving an efficiency of 50.0 % . The value of Q is$ (1) $980 J$ (2) $40 J$ (3) $400 J$ (4) $640 J$ 67. $"Heat cannot be itself flow from a body at lower temperature to a body at higher temperature” is a statement or consequence of:$ (1) $second law of thermodynamics$ (2) $conservation of momentum$ (3) $conservation of mass$ (4) $first law of thermodynamics$ 68. $A 50 g ice cube at - 10^{\circ} C is added to 200 g of water at 30^{\circ} C . The final temperature of the mixture is (specific heat of water = 1 cal g^{- 1} ° C^{- 1}, latent heat of fusion of ice = 80 cal g^{- 1} specific heat of ice = 0.5 cal g^{- 1} ° C^{- 1})$ (1) $20^{\circ} C$ (2) $7^{\circ} C$ (3) $12^{\circ} C$ (4) $10^{\circ} C$ 69. $A solid copper sphere of density ρ, specific heat capacity C and radius r is initially at 200 K . It is suspended inside a chamber whose walls are at 0 K . The time required (in μs) for the temperature of the sphere to drop to 100 K is (σ is Stefan's constant and all the quantities are in SI units.)$ (1) $48 \frac{rρC}{σ}$ (2) $\frac{1}{48} \frac{rρC}{σ}$ (3) $\frac{27}{7} \frac{rρC}{σ}$ (4) $\frac{7}{27} \frac{rρC}{σ}$ 70. $A steel tape of 300 cm length is graduated at 27^{\circ} C . The length of a steel rod measured using the tape is found to be 110 cm at 50^{\circ} C . The actual length of steel rod at 50^{\circ} C is (α_{steel} = 1.2 \times 10^{- 5} K^{- 1})$ (1) $110.03 cm$ (2) $110.10 cm$ (3) $110.07 cm$ (4) $110.62 cm$ 71. $In a Carnot engine, when T_{2} = 0^{o} C and T_{1} = 20 0^{o} C, its efficiency is η_{1} and when T_{1} = 0^{o} C and T_{2} = - 20 0^{o} C, Its efficiency is η_{2}, then what is η_{1} / η_{2}$ (1) $0.577$ (2) $0.733$ (3) $0.638$ (4) $Can not be calculated$ 72. $Pressure of an ideal gas, contained in a closed vessel, is increased by 0.4 % when heated by 1^{\circ} C . Its initial temperature must be:$ (1) $2500 K$ (2) $25^{\circ} C$ (3) $250^{\circ} C$ (4) $250 K$ 73. $An engine has an efficiency of \frac{1}{6} . When the temperature of sink is reduced by 62ºC, its efficiency is doubled. Temperature of the source is:$ (1) $124ºC$ (2) $37ºC$ (3) $62ºC$ (4) $99ºC$ 74. $A monoatomic gas having γ = \frac{5}{3} is stored in a thermally insulated container and the gas is suddenly compressed to (\frac{1}{8})^{th} of its initial volume. The ratio of final pressure and initial pressure is: (γ is the ratio of specific heats of the gas at constant pressure and at constant volume)$ (1) $16$ (2) $32$ (3) $28$ (4) $40$ 75. $A Carnot engine works between a source and a sink maintained at constant temperatures T_{1} and T_{2} . For efficiency to be the greatest$ (1) $T_{1} and T_{2} should be high$ (2) $T_{1} and T_{2} should be low$ (3) $T_{1} should be low and T_{2} should be high$ (4) $T_{1} should be high and T_{2} should be low$ 76. $For which combination of working temperatures the efficiency of Carnot’s engine is highest$ (1) $80 K, 60 K$ (2) $100 K, 80 K$ (3) $60 K, 40 K$ (4) $40 K, 20 K$ 77. $In a Carnot engine, low temperature of reservoir (sink) is 7°C. Its efficiency is 50%. To increase efficiency to 70% by how much temperature of source is to be raised, keeping the temperature of sink constant.$ (1) $840 K$ (2) $280 K$ (3) $560 K$ (4) $373 K$ 78. $If the reading in Fahrenheit scale is twice the reading in Celsius scale, then the reading in Fahrenheit scale is$ (1) $100^{\circ} F$ (2) $120^{\circ} F$ (3) $80^{\circ} F$ (4) $320^{\circ} F$ 79. $The rate of radiation of a black body at 0^{\circ} C is E Js^{- 1} . The rate of radiation of the black body at 273^{\circ} C will be$ (1) $E Js^{- 1}$ (2) $4 E Js^{- 1}$ (3) $\frac{E}{2} Js^{- 1}$ (4) $16 EJs^{- 1}$ 80. $M kg of water at t^{\circ} C is divided into two parts so that one part of mass mkg when converted into ice at 0^{\circ} C would release enough heat to vapourise the other part, then \frac{m}{M} is equal to. (Specific heat of water = 1 cal g^{- 1} ° C^{- 1}, Latent heat of fusion of ice = 80 cal g^{- 1}, Latent heat of steam = 540 cal g^{- 1})$ (1) $640 - t$ (2) $\frac{720 - t}{640}$ (3) $\frac{640 + t}{720}$ (4) $\frac{640 - t}{720}$ 81. $A bicycle tyre is filled with air having pressure of 270 kPa at 27°C. The approximate pressure of the air in the tyre when the temperature increases to 36°C is$ (1) $270kPa$ (2) $262 KPa$ (3) $278 kPa$ (4) $360 kPa$ 82. $Match the List I with List II List - I (A) Triatomic rigid gas (B) Diatomic non-rigid gas (C) Monoatomic gas (D) Diatomic rigid gas List II (I) \frac{C _{p}}{C _{v}} = \frac{5}{3} (II) \frac{C _{p}}{C _{v}} = \frac{7}{5} (III) \frac{C _{p}}{C _{v}} = \frac{4}{3} (IV) \frac{C _{p}}{C _{v}} = \frac{9}{7} Choose the correct answer from the options given below:$ (1) $A-III, B-IV, C-I, D-II$ (2) $A-II, B-IV, C-I, D-III$ (3) $A-IV, B-II, C-III, D-I$ (4) $A-III, B-II, C-IV, D-I$ 83. $During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature. The ratio of \frac{C _{p}}{C _{v}} for the gas is:$ (1) $\frac{5}{3}$ (2) $\frac{3}{2}$ (3) $\frac{7}{5}$ (4) $\frac{9}{7}$ 84. $The helium and argon are put in the flask at the same room temperature (300 K). The ratio of average kinetic energies (per molecule) of helium and argon is: (Give: Molar mass of helium = 4 g / mol, Molar mass of argon = 40 g / mol)$ (1) $1 : 10$ (2) $10 : 1$ (3) $1 : 10$ (4) $1 : 1$ 85. $During the melting of a slab of ice at 273 K at atmospheric pressure:$ (1) $Internal energy of ice-water system remains unchanged.$ (2) $Positive work is done by the ice-water system on the atmosphere.$ (3) $Positive work is done on the ice-water system by the atmosphere.$ (4) $Internal energy of the ice-water system decreases.$ 86. $In an adiabatic process, the density of a diatomic gas becomes 32 times its initial value. The final pressure of the gas is found to be n times the initial pressure. The value of n is$ (1) $128$ (2) $32$ (3) $\frac{1}{32}$ (4) $326$ 87. $An office room contains about 2000 moles of air, The change in the internal energy of this much air when it is cooled from 34^{\circ} C to 24^{\circ} C at a constant pressure of 1.0 atm is [Use γ_{air} = 1.4 and universal gas constant = 8.314 J / mol - K]$ (1) $- 1.9 \times 10^{5} J$ (2) $+ 1.9 \times 10^{5} J$ (3) $- 4.2 \times 10^{5} J$ (4) $+ 0.7 \times 10^{5} J$ 88. $The efficiency of Carnot engine is 50% and temperature of sink is 500 K. If temperature of source is kept constant and its efficiency raised to 60%, then the required temperature of sink will be$ (1) $100 K$ (2) $600 K$ (3) $400 K$ (4) $500 K$ 89. $A diatomic gas (γ = 1.4) does 200 J of work when it is expanded isobarically. The heat given to the gas in the process is:$ (1) $850 J$ (2) $800 J$ (3) $600 J$ (4) $700 J$ 90. $Match with List - II. List - I (A) Heat capacity of body (B) Specific heat capacity of body (C) Latent heat (D) Thermal conductivity List - II (I) J kg^{- 1} (II) J K^{- 1} (III) J kg^{- 1} K^{- 1} (IV) J m^{- 1} K^{- 1} s^{-} Choose the correct answer from the options given$ (1) $(A)-(IV), (B)-(III), (C)-(II), (D)-(I)$ (2) $(A)-(III), (B)-(I), (C)-(II), (D)-(IV)$ (3) $(A)-(III), (B)-(IV), (C)-(I), (D)-(II)$ (4) $(A)-(II), (B)-(III), (C)-(I), (D)-(IV)$