Question 1

A system undergoes a reversible adiabatic process.The entropy change of the system is

Accepted Answer

A) $\Delta$S  0. 
C) $\Delta$S = 0. 
A) $\Delta$S  0. 
C) $\Delta$S = 0. C

Question 2

One mole of a monatomic ideal gas at a pressure of 3.0 atm and a volume of 30 L is isothermally expanded to a pressure of 1.0 atm and a volume of 90 L.Afterwards it is compressed at a constant pressure until its volume is 30 L and then it's pressure is increased at a constant volume back to the original volume of 30 L as shown in the PV diagram.What is the efficiency of this heat engine cycle?

Accepted Answer

A) 0.21 
B) 0.43 
C) 0.57 
D) 0.67 
E) 0.91 
A) 0.21 
B) 0.43 
C) 0.57 
D) 0.67 
E) 0.91 A

Question 3

A coin is tossed five times.What is the probability that the coin lands four times heads up and once as tails?

Accepted Answer

A) 0.031 
B) 0.082 
C) 0.16 
D) 0.25 
E) 0.31 
A) 0.031 
B) 0.082 
C) 0.16 
D) 0.25 
E) 0.31 C

Question 4

A heat engine absorbs 130 kcal of heat and exhausts 74 kcal of heat in each cycle.Calculate the efficiency (in %).It is

Accepted Answer

A) -5.21. 
B) 0. 
C) 5.21. 
D) 22.2. 
E) 43.1. 
A) -5.21. 
B) 0. 
C) 5.21. 
D) 22.2. 
E) 43.1.

Question 5

If a power plant produces steam at 600S1U1P1$\circ$S1S1P0C and outputs heat at 150S1U1P1$\circ$S1S1P0C to a cogeneration power plant that then outputs its exhaust at a temperature of 40S1U1P1$\circ$S1S1P0C.Find the total efficiency of this combination of power plants.Assume both plants are 80% as efficient as a Carnot heat engine.

Accepted Answer

A) 5.9% 
B) 47% 
C) 51% 
D) 53% 
E) 64% 
A) 5.9% 
B) 47% 
C) 51% 
D) 53% 
E) 64%

Question 6

An outboard motor for a boat is cooled by the lake water at 15S1U1P1$\circ$S1S1P0C with a compression ratio of 10.Assume that the air is a diatomic gas.Calculate the efficiency of the Otto cycle.

Accepted Answer

A) 30% 
B) 40% 
C) 50% 
D) 60% 
E) 70% 
A) 30% 
B) 40% 
C) 50% 
D) 60% 
E) 70%

Question 7

A refrigerator has a coefficient of performance of 4.2.If the refrigerator absorbs 55 cal of heat from the cold reservoir (kept at 4S1U1P1$\circ$S1S1P0C)in each cycle,evaluate the heat expelled into the heat reservoir (kept at 21S1U1P1$\circ$S1S1P0C).

Accepted Answer

A) 13 cal 
B) 16 cal 
C) 61 cal 
D) 68 cal 
E) 71 cal 
A) 13 cal 
B) 16 cal 
C) 61 cal 
D) 68 cal 
E) 71 cal

Question 8

Which of the following statements is true?

Accepted Answer

A) An irreversible process cannot be shown on a p-V diagram because the intermediate states are unknown. 
B) The first law of thermodynamics shows that heat added to a system always results in work being done. 
C) An adiabatic process is one which involves no work. 
D) In an isobaric expansion,the temperature does not change. 
E) The second law of thermodynamics does not apply to a closed system. 
A) An irreversible process cannot be shown on a p-V diagram because the intermediate states are unknown. 
B) The first law of thermodynamics shows that heat added to a system always results in work being done. 
C) An adiabatic process is one which involves no work. 
D) In an isobaric expansion,the temperature does not change. 
E) The second law of thermodynamics does not apply to a closed system.

Question 9

A heat pump is operating between two reservoirs at -10S1U1P1$\circ$S1S1P0C and 50S1U1P1$\circ$S1S1P0C.The maximum possible coefficient of performance for the heat pump is

Accepted Answer

A) 1.22. 
B) 2.58. 
C) 4.79. 
D) 5.38. 
E) 9.80. 
A) 1.22. 
B) 2.58. 
C) 4.79. 
D) 5.38. 
E) 9.80.

Question 10

A 1.00-kg iron bar is taken from a forge at 800S1U1P1$\circ$S1S1P0C and dropped into 20.00 kg of water at 15.0S1U1P1$\circ$S1S1P0C.Assuming that no energy is lost by heat to the surroundings as the water/iron reaches their final temperature,determine the total entropy change of the iron bar plus-water system.Assume that specific heat of iron is 448 J/(kg.K).

Accepted Answer

A) 371 J/K 
B) 444 J/K 
C) 534 J/K 
D) 622 J/K 
E) 756 J/K 
A) 371 J/K 
B) 444 J/K 
C) 534 J/K 
D) 622 J/K 
E) 756 J/K

Question 11

A 0.750-kg iron bar is taken from a forge at 900S1U1P1$\circ$S1S1P0C and dropped into 14.00 kg of water at 20.0S1U1P1$\circ$S1S1P0C.Assuming that no energy is lost by heat to the surroundings as the water/iron reaches their final temperature,determine the total entropy change of the water.Assume that specific heat of iron is 448 J/(kg.K).

Accepted Answer

A) -444 J/K 
B) -614 J/K 
C) -756 J/K 
D) -534J/K 
E) 444 J/K 
A) -444 J/K 
B) -614 J/K 
C) -756 J/K 
D) -534J/K 
E) 444 J/K

Question 12

A Carnot engine operates between two reservoirs at 550 K and 250 K.It transfers 300 J to the reservoir at low temperature.The amount of work done is

Accepted Answer

A) 300 J. 
B) 360 J. 
C) 545 J. 
D) 602 J. 
E) 790 J. 
A) 300 J. 
B) 360 J. 
C) 545 J. 
D) 602 J. 
E) 790 J.

Question 13

A scientist looking at a very small,isolated,system observes that the entropy of the system spontaneously decreases while he is looking at it.If true,is this a Nobel-winning discovery or is this not that significant?

Accepted Answer

A) Yes. 
B) No.entropy naturally tends to decrease with time. 
C) No,such fluctuations are allowed in small systems. 
A) Yes. 
B) No.entropy naturally tends to decrease with time. 
C) No,such fluctuations are allowed in small systems.

Question 14

Burning of fuel transfers 4 * 105 W of power into the engine of a 2000-kg vehicle.Suppose the engine has an efficiency of 25% and the vehicle reaches a maximum speed of 32.6 m/s.Assuming the vehicle starts from rest,how long does it take the vehicle to reach this speed?

Accepted Answer

A) 15 seconds 
B) 5.0 seconds 
C) 13 seconds 
D) 9.2 seconds 
E) 11 seconds 
A) 15 seconds 
B) 5.0 seconds 
C) 13 seconds 
D) 9.2 seconds 
E) 11 seconds

Question 15

You have just bought a Carnot refrigerator to keep your food cold.If you intend to run your refrigerator between the cold temperature reservoir at 2.0S1U1P1$\circ$S1S1P0C (the inside of the box)and the high temperature reservoir at 26S1U1P1$\circ$S1S1P0C (your kitchen temperature)how much work will be needed to draw 15 J of heat from the cold reservoir?

Accepted Answer

A) 1.2 J 
B) 1.3 J 
C) 1.4 J 
D) 1.5 J 
A) 1.2 J 
B) 1.3 J 
C) 1.4 J 
D) 1.5 J

Question 16

A car uses 8 liters of gas/hr and does 1.8 kW of useful work.What is the efficiency of the car? (The heat of combustion for 1 liter of gasoline is 3.6 * 106 J.)

Accepted Answer

A) 23% 
B) 34% 
C) 37% 
D) 58% 
E) 69% 
A) 23% 
B) 34% 
C) 37% 
D) 58% 
E) 69%

Question 17

A water cooled engine produces 1000 W of power.The engine's thermal efficiency is 36.4% and the rate of water flow is 100.If water enters the engine block at 15S1U1P1$\circ$S1S1P0C,what is the exit temperature of water?

Accepted Answer

A) 63S1U1P1$\circ$S1S1P0C 
B) 85S1U1P1$\circ$S1S1P0C 
C) 25S1U1P1$\circ$S1S1P0C 
D) 30S1U1P1$\circ$S1S1P0C 
E) 46S1U1P1$\circ$S1S1P0C 
A) 63S1U1P1$\circ$S1S1P0C 
B) 85S1U1P1$\circ$S1S1P0C 
C) 25S1U1P1$\circ$S1S1P0C 
D) 30S1U1P1$\circ$S1S1P0C 
E) 46S1U1P1$\circ$S1S1P0C

Question 18

An engine takes in 600 J of heat from the high temperature reservoir and exhausts 400 J to the low temperature reservoir.What is the efficiency of this engine?

Accepted Answer

A) 25.0% 
B) 33.3% 
C) 40.0% 
D) 60.0% 
A) 25.0% 
B) 33.3% 
C) 40.0% 
D) 60.0%

Question 19

500-g of water at 100S1U1P1$\circ$S1S1P0C is changed into steam at 100S1U1P1$\circ$S1S1P0C at constant pressure.The change in entropy of the water is

Accepted Answer

A) 3.03 kJ/K. 
B) 6.06 kJ/K. 
C) 8.98 kJ/K. 
D) 12.5 kJ/K. 
E) 19.8 kJ/K. 
A) 3.03 kJ/K. 
B) 6.06 kJ/K. 
C) 8.98 kJ/K. 
D) 12.5 kJ/K. 
E) 19.8 kJ/K.

Question 20

Imagine dividing a box into two equal parts,part A on the left and part B on the right.Four identical gas atoms,numbered 1 through 4,are placed in the box.How many distinct microscopic states result in two of the atoms being in part A and the other two atoms in part B?

Accepted Answer

A) 4 
B) 6 
C) 12 
D) 16 
E) 24 
A) 4 
B) 6 
C) 12 
D) 16 
E) 24

Exam 20: The Second Law of Thermodynamics

A system undergoes a reversible adiabatic process.The entropy change of the system is

A coin is tossed five times.What is the probability that the coin lands four times heads up and once as tails?

A heat engine absorbs 130 kcal of heat and exhausts 74 kcal of heat in each cycle.Calculate the efficiency (in %).It is

An outboard motor for a boat is cooled by the lake water at 15 ∘\circ∘ C with a compression ratio of 10.Assume that the air is a diatomic gas.Calculate the efficiency of the Otto cycle.

A refrigerator has a coefficient of performance of 4.2.If the refrigerator absorbs 55 cal of heat from the cold reservoir (kept at 4 ∘\circ∘ C)in each cycle,evaluate the heat expelled into the heat reservoir (kept at 21 ∘\circ∘ C).

Which of the following statements is true?

A heat pump is operating between two reservoirs at -10 ∘\circ∘ C and 50 ∘\circ∘ C.The maximum possible coefficient of performance for the heat pump is

A Carnot engine operates between two reservoirs at 550 K and 250 K.It transfers 300 J to the reservoir at low temperature.The amount of work done is

A scientist looking at a very small,isolated,system observes that the entropy of the system spontaneously decreases while he is looking at it.If true,is this a Nobel-winning discovery or is this not that significant?

Burning of fuel transfers 4 * 105 W of power into the engine of a 2000-kg vehicle.Suppose the engine has an efficiency of 25% and the vehicle reaches a maximum speed of 32.6 m/s.Assuming the vehicle starts from rest,how long does it take the vehicle to reach this speed?

A car uses 8 liters of gas/hr and does 1.8 kW of useful work.What is the efficiency of the car? (The heat of combustion for 1 liter of gasoline is 3.6 * 106 J.)

A water cooled engine produces 1000 W of power.The engine's thermal efficiency is 36.4% and the rate of water flow is 100.If water enters the engine block at 15 ∘\circ∘ C,what is the exit temperature of water?

An engine takes in 600 J of heat from the high temperature reservoir and exhausts 400 J to the low temperature reservoir.What is the efficiency of this engine?

500-g of water at 100 ∘\circ∘ C is changed into steam at 100 ∘\circ∘ C at constant pressure.The change in entropy of the water is

Imagine dividing a box into two equal parts,part A on the left and part B on the right.Four identical gas atoms,numbered 1 through 4,are placed in the box.How many distinct microscopic states result in two of the atoms being in part A and the other two atoms in part B?

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An outboard motor for a boat is cooled by the lake water at 15^$\circ$C with a compression ratio of 10.Assume that the air is a diatomic gas.Calculate the efficiency of the Otto cycle.

A refrigerator has a coefficient of performance of 4.2.If the refrigerator absorbs 55 cal of heat from the cold reservoir (kept at 4^$\circ$C)in each cycle,evaluate the heat expelled into the heat reservoir (kept at 21^$\circ$C).

A heat pump is operating between two reservoirs at -10^$\circ$C and 50^$\circ$C.The maximum possible coefficient of performance for the heat pump is

Burning of fuel transfers 4 * 10⁵ W of power into the engine of a 2000-kg vehicle.Suppose the engine has an efficiency of 25% and the vehicle reaches a maximum speed of 32.6 m/s.Assuming the vehicle starts from rest,how long does it take the vehicle to reach this speed?

A car uses 8 liters of gas/hr and does 1.8 kW of useful work.What is the efficiency of the car? (The heat of combustion for 1 liter of gasoline is 3.6 * 10⁶ J.)

A water cooled engine produces 1000 W of power.The engine's thermal efficiency is 36.4% and the rate of water flow is 100.If water enters the engine block at 15^$\circ$C,what is the exit temperature of water?

500-g of water at 100^$\circ$C is changed into steam at 100^$\circ$C at constant pressure.The change in entropy of the water is