Thermodynamics PYQs Set 9 (PDF)

Set 9 of 16 · Questions 241-270 of 459

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Mere Teacher · Previous Year Questions NEET Physics · Thermodynamics · Set 9 (Q241-270)
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241. $A Carnot's engine used first an ideal monoatomic gas then an ideal diatomic gas. If the source and sink temperature are 41 1^{o} C and 6 9^{o} C respectively and the engine extracts 1000 J of heat in each cycle, then area enclosed by the PV diagram is$ (1) $100 J$ (2) $300 J$ (3) $500 J$ (4) $700 J$ 242. $A metal cube absorbs 2100.0 J of heat when its temperature is raised by 2^{\circ} C . If the specific heat of the metal is 900 J kg^{- 1} K^{- 1}, then the mass of the cube is$ (1) $1.116 kg$ (2) $2.33 kg$ (3) $1.66 kg$ (4) $1.33 kg$ 243. $Consider a reversible engine of ecoefficiency \frac{1}{6} . When the temperature of the sink is reduced by 62^{\circ} C, its efficiency gets doubled, The temperature of the source and sink respectively are$ (1) $372 K and 310 K$ (2) $273 K and 300 K$ (3) $99^{\circ} C and 10^{\circ} C$ (4) $200^{\circ} C and 37^{\circ} C$ 244. $An ideal gas at 127^{\circ} C is compressed suddenly to \frac{8}{27} of its initial volume. If γ = \frac{5}{3} for an ideal gas, then rise in its temperature is$ (1) $450 K$ (2) $500 K$ (3) $225 K,$ (4) $405 K$ 245. $A sample of 0.1 g of water at 100^{\circ} C and normal pressure (1.013 \times 10^{5} Nm^{- 2}) requires 54 cal of heat energy to convert to steam at 100^{\circ} C . If the volume of the steam produced is 167.1 cc, the change in internal energy of the sample is [NEET 2018]$ (1) $42.2 J$ (2) $208.7 J$ (3) $104.3 J$ (4) $84.5 J$ 246. $The coefficient of performance of refrigerator, whose efficiency is 25% is$ (1) $1$ (2) $3$ (3) $5$ (4) $7$ 247. $An ideal gas in a cylinder is compressed adiabatically to one-third of its original volume. A work of 45 J is done on the gas by the process. The change in internal energy of the gas and the heat flowed into the gas, respectively are$ (1) $45 J and zero$ (2) $- 45 J and zero$ (3) $45 J and heat flows out of the gas$ (4) $- 45 J and heat flows into the gas$ 248. $Two vessels separately contain two ideal gases A and B at the same temperature, the pressure of A being twice that ofB . Under such conditions, the density of A is found to be 1.5 times the density ofB . The ratio of molecular weight ofA and B is$ (1) $2$ (2) $\frac{1}{2}$ (3) $\frac{2}{3}$ (4) $\frac{3}{4}$ 249. $A metal cooking pot has a base area of 0.2 m^{2} and thickness 2.0 cm . It boils water at a rate of 3.0 kg / min when placed on a hot plate. The temperature of the part of the lot plate in contact with the pot is approximately [Thermalconductivity of metal is 120 Js^{- 1} m^{- 1} K^{- 1}, heat of vaporisation of water is 2 \times 10^{6} J / kg]$ (1) $246^{\circ} C$ (2) $183^{\circ} C$ (3) $162^{\circ} C$ (4) $214^{\circ} C$ 250. $The internal energy change in a system that has absorbed 2 kcal of heat and done 500 J ofwork is$ (1) $6400 J$ (2) $5400 J$ (3) $7900 J$ (4) $8900 J$ 251. $A hunter fired a metallic bullet of mass mkg from a gun towards an obstacle and it just melts when it is stopped by the obstacle. The initial temperature of the bullet is 300 K . If \frac{1}{4} th of heat is absorbed by the obstacle, then the minimum velocity of the bullet is (Melting point of bullet = 600 K, Specific heat of bullet = 0.03 cal g^{- 1} ° C^{- 1},Latent heat of fusion of bullet = 6 cal g^{- 1})$ (1) $410 ms^{- 1}$ (2) $260 ms^{- 1}$ (3) $460 ms^{- 1}$ (4) $310 ms^{- 1}$ 252. $A calorimeter contains 0.5 kg of water at 30^{\circ} C . When 0.3 kg of water at 60^{\circ} C is added to it, the resulting temperature is found to be 40^{\circ} C . The water equivalent of the calorimeter is$ (1) $0.25 kg$ (2) $0.1 kg$ (3) $0.2 kg$ (4) $0.3kg$ 253. $Work done by a Carnot engine operating between temperatures 127 °C and 27 °C is 2 kJ. The amount of heat transferred to the engine by the reservoir is:$ (1) $8 kJ$ (2) $2.67kJ$ (3) $2 kJ$ (4) $4 kJ$ 254. $The heat energy released by water of mass 2 kg when it is cooled by 10^{\circ} C is (Specific heat capacity of water = 4200 J kg^{- 1} K^{- 1})$ (1) $42000 J$ (2) $21000 J$ (3) $63000 J$ (4) $84000 J$ 255. $In a mechanical refrigerator, the low temperature coils are at a temperature of - 23°C and the compressed gas in the condenser has a temperature of 27°C. The theoretical coefficient of performance is$ (1) $5$ (2) $8$ (3) $6$ (4) $6.5$ 256. $Efficiency of a Carnot engine is 50% when temperature of outlet is 500 K. In order to increase efficiency up to 60% keeping temperature of intake the same what is temperature of outlet$ (1) $200 K$ (2) $400 K$ (3) $600 K$ (4) $800 K$ 257. $A Carnot's engine operates with source at 127^{\circ} C and sink at 27^{\circ} C . If the source supplies 40 kJ of heat energy, the work done by the engine is$ (1) $30 kJ$ (2) $10 kJ$ (3) $4 kJ$ (4) $1 kJ$ 258. $Boiling water is changing into steam. The specific heat of boiling water is$ (1) $zero$ (2) $one$ (3) $infinity$ (4) $less than one$ 259. $A gas at N.T.P. is suddenly compressed to (\frac{1}{4})^{th} of its original volume. The final pressure in (Given γ = ratio of specific heats = \frac{3}{2}) atmosphere is (P = original pressure)$ (1) $4 P$ (2) $\frac{3}{2} P$ (3) $8 P$ (4) $1 4 P$ 260. $A total of 48 J heat is given to one mole of helium kept in a cylinder. The temperature of helium increases by 2^{\circ} C . The work done by the gas is: Given, R = 8.3 J K^{- 1} mol^{- 1} .$ (1) $24.9 J$ (2) $72.9 J$ (3) $48 J$ (4) $23.1J$ 261. $The equation for real gas is given by (P + \frac{a}{V ^{2}}) (V - b) = RT, where P, V, T and R are the pressure, volume, temperature and gas constant, respectively. The dimension of ab^{- 2} is equivalent to that of:$ (1) $Compressibility$ (2) $Planck's constant$ (3) $Energy density$ (4) $Strain$ 262. $At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth’s atmosphere? (Given: Mass of oxygen molecule (m) = 2.76 \times 1 0^{- 26} kg, Boltzmann’s constant k_{B} = 1.38 \times 1 0^{- 23} J K^{- 1})$ (1) $2.518 \times 1 0^{4} K$ (2) $8.360 \times 1 0^{4} K$ (3) $5.016 \times 1 0^{4} K$ (4) $1.254 \times 1 0^{4} K$ 263. $The efficiency of a Carnot engine which operates between the two temperatures T_{1} = 500 K and T_{2} = 300 K is$ (1) $25 %$ (2) $40 %$ (3) $50 %$ (4) $75 %$ 264. $A refrigerator is to maintain eatables kept inside at 7°C. The coefficient of performance of refrigerator if room temperature is 38°C is$ (1) $15.5$ (2) $16.3$ (3) $20.1$ (4) $9.03$ 265. $A thermos flask contains 250 g of coffee at 90^{\circ} C . To this 20 g oí milk at 5^{\circ} C is added. After equilibrium is established, the temperature of the liquid is (Assume no heat loss to the thermos bottle. Take specific heat of coffee and milk as 1.00 cal / g^{\circ} C)$ (1) $3.23^{\circ} C$ (2) $3.15^{\circ} C$ (3) $83.7^{\circ} C$ (4) $37.8^{\circ} C$ 266. $Which of the following is not a thermodynamic co-ordinate?$ (1) $Gas constant (R)$ (2) $Pressure (P)$ (3) $Volume (V)$ (4) $Temperature (T)$ 267. $The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is$ (1) $26.8%$ (2) $20%$ (3) $6.25%$ (4) $12.5%$ 268. $A polyatomic gas follows a law T^{2} Vα = constant. Find α for which the heat exchange of gas in the process becomes zero.$ (1) $α = \frac{3}{2}$ (2) $α = \frac{2}{3}$ (3) $α = \frac{4}{3}$ (4) $α = \frac{3}{4}$ 269. $The coefficient of performance of a refrigerator is 5. If the temperature inside freezer is - 2 0^{o} C, the temperature ofthe surroundings to which it rejects heat is$ (1) $1 1^{o} C$ (2) $2 1^{o} C$ (3) $3 1^{o} C$ (4) $4 1^{o} C$ 270. $If the ratio of densities of two substances is 5:6 and the ratio of their specific heat capacities is 3 : 5, then the ratio of heat energies required per unit volume so that the two substances can have same temperature rise is$ (1) $1 : 1$ (2) $1 : 4$ (3) $1 : 2$ (4) $1 : 3$