Thermodynamics PYQs Set 4 (PDF)

Set 4 of 16 · Questions 91-120 of 459

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Mere Teacher · Previous Year Questions NEET Physics · Thermodynamics · Set 4 (Q91-120)
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91. $The pressure and density of a diatomic gas (γ = \frac{7}{5}) changes adiabatically from (P, ρ) to (P^{’}, r^{’}) . If \frac{ρ ^{’}}{ρ} = 32 then \frac{P ^{’}}{P} should be$ (1) $\frac{1}{128}$ (2) $128$ (3) $32$ (4) $64$ 92. $An engine performs 2000 J of mechanical work and discards 4000 J of heat each cycle. What is the thermal efficiency of the engine?$ (1) $45.5 %$ (2) $31.4 %$ (3) $25 %$ (4) $33.3 %$ 93. $If two rods of length L and 2 L, having coefficients of linear expansion α and 2 α respectively are connected end-to-end, then find the average coefficient of linear expansion of the composite rod.$ (1) $\frac{3 α}{2}$ (2) $\frac{5 α}{2}$ (3) $\frac{5 α}{4}$ (4) $\frac{5 α}{3}$ 94. $A gas is expanded from an initial state to a final state along a path that consists of (a) an isothermal expansion doing 40 J work, (b) an adiabatic expansion doing W work, (c) an isothermal expansion doing 30 J work. If the total change in the internal energy of the gas is -20 J, the work done by the gas during the adiabatic expansion W =$ (1) $50 J$ (2) $90 J$ (3) $70 J$ (4) $20 J$ 95. $Two metallic spheres P and Q are made of same material have same smoothness but the weight of P is 8 times that of Q . If the two are heated to same temperature and left to cool, then the ratio of rate of cooling of Q to that of P is$ (1) $4$ (2) $8$ (3) $2$ (4) $1$ 96. $The heat energy supplied to a diatomic gas at constant pressure is 210 J, then the work done by the gas is$ (1) $60 J$ (2) $150 J$ (3) $90 J$ (4) $210 J$ 97. $A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency?$ (1) $380 K$ (2) $275 K$ (3) $325 K$ (4) $250 K$ 98. $A body cools down from 75^{\circ} C to 60^{\circ} C in 10 minutes. It will cool down from 65^{\circ} C to 55^{\circ} C in a time$ (1) $10 minutes$ (2) $Less than 10 minutes$ (3) $More than 10 minutes$ (4) $Less than or more than 10 minutes depending on its mass$ 99. $The specific heat capacity of a copper block of mass M is 's'. If the mass of the copper block is doubled, the specific heat capacity will be$ (1) $2 s$ (2) $\frac{s}{2}$ (3) $s$ (4) $3 2 s$ 100. $One mole of an ideal gas requires 207 J heat to rise the temperature by 10 K when heated at constant pressure. If the same gas is heated at constant volume to raise the temperature by the same 10 K, the heat required is (Given the gas constant R = 8.3 J/mole K)$ (1) $198.7 J$ (2) $29 J$ (3) $215.3 J$ (4) $124 J$ 101. $If the door of a refrigerator is kept open, then which of the following is true$ (1) $Room is cooled$ (2) $Room is heated$ (3) $Room is either cooled or heated$ (4) $Room is neither cooled nor heated$ 102. $A cup of coffee cools from 150^{\circ} F to 144^{\circ} F in 1 min in a room temperature at 72^{\circ} F . How much time with the coffee take to cool from 110^{\circ} F to 104^{\circ} F in the same room?$ (1) $1.55 min$ (2) $2.14 min$ (3) $2.89 min$ (4) $3.35 min$ 103. $A diatomic gas (γ = 1.4) does 300 J work when it is expanded isobarically. The heat given to the gas in this process is$ (1) $1050 J$ (2) $950 J$ (3) $600 J$ (4) $550 J$ 104. $A gas expands with temperature according to the relation, V = k T^{2/3}, where k is a constant. Work done when the temperature changes by 60 K is (R = universal gas constant.)$ (1) $10 R$ (2) $20 R$ (3) $50 R$ (4) $40 R$ 105. $A Carnot engine, having an efficiency of η = 1/10 as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is$ (1) $99 J$ (2) $90 J$ (3) $1 J$ (4) $100 J$ 106. $The efficiency of a Carnot engine operating with reservoir temperatures of 10 0^{0} C and - 2 3^{0} C will be -$ (1) $\frac{100 - 23}{100}$ (2) $\frac{100 + 23}{100}$ (3) $\frac{100 + 23}{373}$ (4) $\frac{100 - 23}{373}$ 107. $0.08 kg air is heated at constant volume through 5^{\circ} C . The specific heat of air at constant volume is 0.17 kcal / kg^{\circ} C and J = 4.18 joule / cal . The change in its internal energy is approximately.$ (1) $318 J$ (2) $298 J$ (3) $284 J$ (4) $142 J$ 108. $Two Carnot engines A and B are operated in series. The engine A receives heat from the source at temperature T_{1} and rejects the heat to the sink at temperature T . The second engine B receives the heat at temperature T and rejects to its sink at temperature T_{2} . For what value of T the efficiencies ofthe two engines are equal$ (1) $\frac{T _{1} - T _{2}}{2}$ (2) $T_{1} T_{2}$ (3) $T_{1} T_{2}$ (4) $\frac{T _{1} + T _{2}}{2}$ 109. $In a process, the work done by the system is equal to the decrease in its internal energy. The process that the system undergoes is$ (1) $isothermal process$ (2) $adiabatic process$ (3) $isobaric process$ (4) $isochoric process$ 110. $An ideal gas heat engine operates in Cannot cycle between 227ºC and 127ºC. It absorbs 6 \times 1 0^{4} cal of heat at higher temperature. Amount of heat converted to work is:$ (1) $2.4 \times 1 0^{4} cal$ (2) $6 \times 1 0^{4} cal$ (3) $1.2 \times 1 0^{4} cal$ (4) $4.8 \times 1 0^{4} cal$ 111. $A Carnot engine working between 300 K and 400 K has 800 J of useful work. The amount of heat energy supplied to the engine from the source is$ (1) $2400 J$ (2) $3200 J$ (3) $1200 J$ (4) $3600 J$ 112. $A certain amount of gas of volume V at 27°C temperature and pressure 2 x 107 N m^{- 2} expands isothermally until its volume gets doubled. Later it expands adiabatically until its volume gets redoubled. The final pressure of the gas will be (Use γ =1.5)$ (1) $3.536 x 1 0^{5} Pa$ (2) $3.536 x 1 0^{6} Pa$ (3) $1.25 x 1 0^{6} Pa$ (4) $1.25 x 1 0^{5} Pa$ 113. $There is no change in internal energy of an ideal gas when it undergoes$ (1) $isothermal expansion$ (2) $adiabatic expansion$ (3) $free expansion$ (4) $isobaric expansion$ 114. $For a reversible process, necessary condition is$ (1) $In the whole cycle of the system, the loss of any type of heat energy should be zero$ (2) $That the process should be too fast$ (3) $That the process should be slow so that the working substance should remain in thermal and mechanical equilibrium with the surroundings$ (4) $The loss of energy should be zero and it should be quasistatic$ 115. $Given are statements for certain thermodynamic variables, (A) Internal energy, volume (V) and mass (M) are extensive variables. (B) Pressure (P), temperature (T) and density ( ρ ) are intensive variables. (C) Volume (V), temperature (T) and density ( ρ ) are intensive variables. (D) Mass (M), temperature (T) and internal energy are extensive variables. Choose the correct answer from the options given below:$ (1) $(B) and (C) Only$ (2) $(C) and (D) Only$ (3) $(D) and (A) Only$ (4) $(A) and (B) Only$ 116. $A given sample of an ideal gas occupies a volume V at a pressure P and absolute temperature T . The mass ofeach molecule ofthe gas is m . Which ofthe following gives the density of the gas?$ (1) $P / (kT)$ (2) $Pm / (kT)$ (3) $P / (kT \nabla)$ (4) $mkT$ 117. $If an ideal flask containing hot coffee is shaken, the temperature of the coffee will:$ (1) $decrease$ (2) $increase$ (3) $remain same$ (4) $decrease if temperature is below 4ºC and increase if temperature is equal to or more than 4ºC$ 118. $One mole of ideal gas goes through a process p V^{3} = constant, where p and V are pressure and volume, respectively. Let W be the work done by the gas as its temperature is increased by Δ T . The value of \| W \| is (R is the universal gas constant.)$ (1) $R Δ T$ (2) $\frac{1}{3} R Δ T$ (3) $R^{3} Δ T$ (4) $\frac{R}{2} Δ T$ 119. $The length of a metal rod at 30^{\circ} C is 30 cm . If its temperature is raised to 105^{\circ} C, its length is increased by 0.027 cm . Then the coefficient of linear expansion of the metal is$ (1) $12 \times 10^{- 4} /° C$ (2) $12 \times 10^{- 5} /° C$ (3) $12 \times 10^{- 6} /° C$ (4) $12 \times 10^{- 7} /° C$ 120. $If a steam engine delivers 6.0 \times 1 0^{8} J of work per minute and absorbs 5.4 \times 1 0^{9} J of heat per minute from its boiler then efficiency of the engine is$ (1) $11%$ (2) $12%$ (3) $13%$ (4) $14%$