Question 1

If an engine takes in 600 J of heat and puts out 200 J of heat,what is its efficiency?

Accepted Answer

A) 33% 
B) 25% 
C) 75% 
D) 10% 
E) 67% 
A) 33% 
B) 25% 
C) 75% 
D) 10% 
E) 67%

Question 2

A solid mass of aluminum is at its melting point.During the melting process,the change in entropy of the aluminum is 9.11 * 10-3 kJ/K.What is the mass of the aluminum?

Accepted Answer

A) 20.0 g 
B) 28.9 g 
C) 23.7 g 
D) 21.4 g 
E) 26.3 g 
A) 20.0 g 
B) 28.9 g 
C) 23.7 g 
D) 21.4 g 
E) 26.3 g

Question 3

You have just bought a Carnot refrigerator to keep your frozen vegetables frozen.If you intend to run your refrigerator between the cold temperature reservoir at -5S1U1P1$\circ$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) 1.1 J 
B) 1.2 J 
C) 1.6 J 
D) 1.7 J 
A) 1.1 J 
B) 1.2 J 
C) 1.6 J 
D) 1.7 J

Question 4

An engine takes in 600 J of heat from the high temperature reservoir and has an efficiency of 25%.How much heat does it exhaust to the cold reservoir?

Accepted Answer

A) 400 J 
B) 150 J 
C) 200 J 
D) 650 J 
A) 400 J 
B) 150 J 
C) 200 J 
D) 650 J

Question 5

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) 534 J/K 
C) 756 J/K 
D) 622 J/K 
E) 995 J/K 
A) 444 J/K 
B) 534 J/K 
C) 756 J/K 
D) 622 J/K 
E) 995 J/K

Question 6

Burning of fuel transfers 4 * 105 W of power into the engine of a 2000-kg vehicle;supposing that the engine is 25% efficient,determine the maximum speed the vehicle can achieve 5 seconds after starting from rest.

Accepted Answer

A) 32.6 m/s 
B) 10.5 m/s 
C) 22.4 m/s 
D) 5.8 m/s 
E) 16.4 m/s 
A) 32.6 m/s 
B) 10.5 m/s 
C) 22.4 m/s 
D) 5.8 m/s 
E) 16.4 m/s

Question 7

The efficiency of an engine

Accepted Answer

A) can have units of Joules. 
B) is always less than 100%. 
C) is the ratio of the work done by the engine to the heat exhausted to the low temperature reservoir. 
D) is the ratio of the heat exhausted to the low temperature reservoir to the work done by the engine. 
A) can have units of Joules. 
B) is always less than 100%. 
C) is the ratio of the work done by the engine to the heat exhausted to the low temperature reservoir. 
D) is the ratio of the heat exhausted to the low temperature reservoir to the work done by the engine.

Question 8

Burning of fuel transfers 5 * 105 W of power into the engine of a 1500-kg vehicle;suppose the maximum speed the vehicle can achieve 5 seconds after starting from rest is 32.6 m/s.Determine the efficiency of the engine.

Accepted Answer

A) 35% 
B) 25% 
C) 32% 
D) 28% 
E) 20% 
A) 35% 
B) 25% 
C) 32% 
D) 28% 
E) 20%

Question 9

Burning of fuel transfers power into the engine of a 2000-kg vehicle;suppose the engine has an efficiency of 25% and the maximum speed the vehicle can achieve 5 seconds after starting from rest is 32.6 m/s.Determine the power the fuel transfers to the engine.

Accepted Answer

A) 9.0 * 105 W 
B) 5.0 * 105 W 
C) 6.7 * 105 W 
D) 7.8 * 105 W 
E) 8.5 * 105 W 
A) 9.0 * 105 W 
B) 5.0 * 105 W 
C) 6.7 * 105 W 
D) 7.8 * 105 W 
E) 8.5 * 105 W

Question 10

One end of a metal rod is in contact with a reservoir at a 400 K and the other end in contact with a reservoir at 200 K.The rod and reservoirs make up a closed system.If 5500 J are conducted from one end to the other uniformly (no change in temperature along the rod)what is the change in entropy of the 200 K reservoir?

Accepted Answer

A) 27.5 J/K 
B) 10.5 J/K 
C) 13.8 J/K 
D) 0.00 J/K 
E) 8.56 J/K 
A) 27.5 J/K 
B) 10.5 J/K 
C) 13.8 J/K 
D) 0.00 J/K 
E) 8.56 J/K

Question 11

A 16-gram lead bullet slams into a concrete wall and melts on impact.If the temperature of the speeding bullet was 25S1U1P1$\circ$S1S1P0C and if the specific heat of lead is 0.13 kJ/(kgK)and its latent heat of fusion is 23 kJ/kg,what is the change in entropy of the bullet during this process? The melting point of lead is 601K.

Accepted Answer

A) 2.1 J/K 
B) 0.61 J/K 
C) 1.5 J/K 
D) None are correct. 
A) 2.1 J/K 
B) 0.61 J/K 
C) 1.5 J/K 
D) None are correct.

Question 12

Find the ratio of the coefficients of performance for two ideal heat pumps used as heaters for a house.The house is kept at 21S1U1P1$\circ$S1S1P0C in both cases.In case 1 the outside temperature is 4.0S1U1P1$\circ$S1S1P0C,in case 2 the outside temperature is -14S1U1P1$\circ$S1S1P0C.

Accepted Answer

A) 2.1 
B) 2.2 
C) 8.4 
D) 8.8 
E) 17.3 
A) 2.1 
B) 2.2 
C) 8.4 
D) 8.8 
E) 17.3

Question 13

A 145-g snowball,initially at 0S1U1P1$\circ$S1S1P0C,melts in your hands becoming 145 g of water at 20S1U1P1$\circ$S1S1P0C.What is the change in entropy of the snow/water associated with this event? Remember the latent heat of fusion for water is 334 kJ/kg and the specific heat of liquid water is 4.19 kJ/(kgK).

Accepted Answer

A) 0.18 kJ/K 
B) 0.22 kJ/K 
C) 2.0 kJ/K 
D) 3.4 kJ/K 
A) 0.18 kJ/K 
B) 0.22 kJ/K 
C) 2.0 kJ/K 
D) 3.4 kJ/K

Question 14

Your Carnot refrigerator has a coefficient of performance of 5.4.Assume that 15.0 J of heat are removed from the cold refrigerator compartment in each engine cycle.What is the heat expelled into the kitchen for each cycle?

Accepted Answer

A) 2.8 J 
B) 12.2 J 
C) 15.0 J 
D) 15.4 J 
E) 17.8 J 
A) 2.8 J 
B) 12.2 J 
C) 15.0 J 
D) 15.4 J 
E) 17.8 J

Question 15

An engine operates with an efficiency of 0.5.Which of the following temperatures cannot represent the temperatures of the hot and the cold reservoirs be respectively?

Accepted Answer

A) TH = 600 K and TC = 100 
B) TH = 600 K and TC = 200 
C) TH = 500 K and TC = 200 
D) TH = 500 K and TC = 300 
A) TH = 600 K and TC = 100 
B) TH = 600 K and TC = 200 
C) TH = 500 K and TC = 200 
D) TH = 500 K and TC = 300

Question 16

One end of a metal rod is in contact with a reservoir at a 400 K and the other end in contact with a reservoir at 100 K.The rod and reservoirs make up a closed system.If 5500 J are conducted from one end to the other uniformly (no change in temperature along the rod)what is the change in entropy of the 400 K reservoir?

Accepted Answer

A) 10.5 J/K 
B) 8.56 J/K 
C) 0.00 J/K 
D) -11.8 J/K 
E) -13.8 J/K 
A) 10.5 J/K 
B) 8.56 J/K 
C) 0.00 J/K 
D) -11.8 J/K 
E) -13.8 J/K

Question 17

What size heat pump with a coefficient of performance of 4.0 is needed for a home that loses heat energy at a rate of 12 kW on the coldest day of the year?

Accepted Answer

A) 3.0 kW 
B) 4.0 kW 
C) 6.0 kW 
D) 12 kW 
E) 48 kW 
A) 3.0 kW 
B) 4.0 kW 
C) 6.0 kW 
D) 12 kW 
E) 48 kW

Question 18

An ideal-gas heat engine operates in a Carnot cycle between temperatures of 266S1U1P1$\circ$S1S1P0C and 115S1U1P1$\circ$S1S1P0C.It absorbs 4250 cal per cycle at 266S1U1P1$\circ$S1S1P0C.What is its efficiency in %?

Accepted Answer

A) 28% 
B) 36% 
C) 44% 
D) 79% 
E) 100% 
A) 28% 
B) 36% 
C) 44% 
D) 79% 
E) 100%

Question 19

You toss two dice;the total number of ways you can get 12 is

Accepted Answer

A) 1. 
B) 2. 
C) 3. 
D) 4. 
E) 6. 
A) 1. 
B) 2. 
C) 3. 
D) 4. 
E) 6.

Question 20

A water cooled engine produces 1000 W of power.Water enters the engine block at 15S1U1P1$\circ$S1S1P0C and exits at 30S1U1P1$\circ$S1S1P0C.The rate of water flow is 100 L/hr.What is the engine's thermal efficiency?

Accepted Answer

A) 63.6% 
B) 36.4% 
C) 50% 
D) 10% 
E) 15% 
A) 63.6% 
B) 36.4% 
C) 50% 
D) 10% 
E) 15%

Exam 20: The Second Law of Thermodynamics

If an engine takes in 600 J of heat and puts out 200 J of heat,what is its efficiency?

A solid mass of aluminum is at its melting point.During the melting process,the change in entropy of the aluminum is 9.11 * 10-3 kJ/K.What is the mass of the aluminum?

An engine takes in 600 J of heat from the high temperature reservoir and has an efficiency of 25%.How much heat does it exhaust to the cold reservoir?

Burning of fuel transfers 4 * 105 W of power into the engine of a 2000-kg vehicle;supposing that the engine is 25% efficient,determine the maximum speed the vehicle can achieve 5 seconds after starting from rest.

The efficiency of an engine

Burning of fuel transfers 5 * 105 W of power into the engine of a 1500-kg vehicle;suppose the maximum speed the vehicle can achieve 5 seconds after starting from rest is 32.6 m/s.Determine the efficiency of the engine.

Burning of fuel transfers power into the engine of a 2000-kg vehicle;suppose the engine has an efficiency of 25% and the maximum speed the vehicle can achieve 5 seconds after starting from rest is 32.6 m/s.Determine the power the fuel transfers to the engine.

Find the ratio of the coefficients of performance for two ideal heat pumps used as heaters for a house.The house is kept at 21 ∘\circ∘ C in both cases.In case 1 the outside temperature is 4.0 ∘\circ∘ C,in case 2 the outside temperature is -14 ∘\circ∘ C.

A 145-g snowball,initially at 0 ∘\circ∘ C,melts in your hands becoming 145 g of water at 20 ∘\circ∘ C.What is the change in entropy of the snow/water associated with this event? Remember the latent heat of fusion for water is 334 kJ/kg and the specific heat of liquid water is 4.19 kJ/(kgK).

Your Carnot refrigerator has a coefficient of performance of 5.4.Assume that 15.0 J of heat are removed from the cold refrigerator compartment in each engine cycle.What is the heat expelled into the kitchen for each cycle?

An engine operates with an efficiency of 0.5.Which of the following temperatures cannot represent the temperatures of the hot and the cold reservoirs be respectively?

What size heat pump with a coefficient of performance of 4.0 is needed for a home that loses heat energy at a rate of 12 kW on the coldest day of the year?

An ideal-gas heat engine operates in a Carnot cycle between temperatures of 266 ∘\circ∘ C and 115 ∘\circ∘ C.It absorbs 4250 cal per cycle at 266 ∘\circ∘ C.What is its efficiency in %?

You toss two dice;the total number of ways you can get 12 is

A water cooled engine produces 1000 W of power.Water enters the engine block at 15 ∘\circ∘ C and exits at 30 ∘\circ∘ C.The rate of water flow is 100 L/hr.What is the engine's thermal efficiency?

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A solid mass of aluminum is at its melting point.During the melting process,the change in entropy of the aluminum is 9.11 * 10^-3 kJ/K.What is the mass of the aluminum?

Burning of fuel transfers 4 * 10⁵ W of power into the engine of a 2000-kg vehicle;supposing that the engine is 25% efficient,determine the maximum speed the vehicle can achieve 5 seconds after starting from rest.

Burning of fuel transfers 5 * 10⁵ W of power into the engine of a 1500-kg vehicle;suppose the maximum speed the vehicle can achieve 5 seconds after starting from rest is 32.6 m/s.Determine the efficiency of the engine.

Find the ratio of the coefficients of performance for two ideal heat pumps used as heaters for a house.The house is kept at 21^$\circ$C in both cases.In case 1 the outside temperature is 4.0^$\circ$C,in case 2 the outside temperature is -14^$\circ$C.

A 145-g snowball,initially at 0^$\circ$C,melts in your hands becoming 145 g of water at 20^$\circ$C.What is the change in entropy of the snow/water associated with this event? Remember the latent heat of fusion for water is 334 kJ/kg and the specific heat of liquid water is 4.19 kJ/(kgK).

An ideal-gas heat engine operates in a Carnot cycle between temperatures of 266^$\circ$C and 115^$\circ$C.It absorbs 4250 cal per cycle at 266^$\circ$C.What is its efficiency in %?

A water cooled engine produces 1000 W of power.Water enters the engine block at 15^$\circ$C and exits at 30^$\circ$C.The rate of water flow is 100 L/hr.What is the engine's thermal efficiency?