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Exam 14: Second Law of Thermodynamics

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Question 21

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An ideal Carnot air conditioner operates between an indoor temperature of 20°C and an outdoor temperature of 39°C.How much energy does it use to remove 2000 J of thermal energy from the interior of the house?

A) 105 J
B) 130 J
C) 780 J
D) 520 J
E) 340 J

F) B) and C)
G) B) and D)

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Question 22

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What is the change in entropy of the ice when a 0.050-kg ice cube at 0°C melts? The latent heat of fusion for water is 80 cal/g.

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Question 23

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A thermodynamic engine having the maximum possible efficiency has an efficiency of 35.0% when operating between two heat reservoirs.If the temperature of the hot reservoir is 700 K,what is the temperature of the cold reservoir?

During each cycle,a thermodynamic engine takes in 4.0 J of energy,does 1.0 J of work,and expels 3.0 J of energy.What is its efficiency?

An ideal Carnot engine operates between a warm reservoir at 233 K and a colder reservoir.During each cycle,this engine extracts $15.0 \mathrm {~J}$ of energy from the warm reservoir and does $4.0 \mathrm {~J}$ of work.What is the temperature of the colder reservoir?

A thermodynamic engine has an efficiency of 31.4% and receives 8.72 kJ of energy per cycle. (a)How much work does it perform in each cycle? (b)How much energy does it exhaust in each cycle?

The "hot shot" thermodynamic engine operating between 40°C and 380°C has an efficiency that is 60% of that of an ideal Carnot engine operating between the same temperatures.If the "hot shot" engine absorbs energy at a rate of 60 kW,at what rate does it exhaust energy?

On a cold winter day,the outside temperature is -20°C and the inside temperature is maintained at 20°C.There is a net thermal energy flow to the outside through the walls,roof,etc.,of 25 kW.At what rate is the entropy of the air outside the house changing as a result of this process?

An irreversible engine operating between the temperatures of 550 K and 300 K extracts 1.20 kJ of thermal energy from the hot reservoir and produces 0.450 kJ of work.How much entropy is created in the process?

A reversible engine takes in energy at a rate of 555 W and exhausts energy at 482 W. (a)How much power does it produce? (b)What is its efficiency? (c)If operated in reverse as a refrigerator,what would be its performance coefficient (COP)?

If the efficiency of a reversible engine is 28%,what is its COP (performance coefficient)operated (a)as a refrigerator,and (b)as a thermodynamic pump?

An ideal Carnot engine is operated as a thermodynamic pump to heat a room in the winter.The thermodynamic pump delivers thermal energy to the room at the rate of 47 kJ per second and maintains the room at a temperature of 293 K when the outside temperature is 237 K.The power requirement to run the thermodynamic pump under these operating conditions is closest to

An important feature of the Carnot cycle is that

A thermodynamic engine absorbs 64 kcal of energy each cycle and exhausts 42 kcal. (a)What is the efficiency of this engine? (b)How much work does this engine do per cycle?

An ideal Carnot thermodynamic engine operates between $285 \mathrm {~K}$ and $460 \mathrm {~K} \text {. }$ What is its efficiency?

An air conditioner with a coefficient of performance of 3.50 uses 30.0 kW of power to operate.What power is it discharging to the outdoors?

A Carnot engine operates between two reservoirs with unknown temperatures.If the Carnot engine operates at $67 \%$ efficiency,what is the ratio of the absolute temperatures of the reservoirs,T_c/T_h?

An ideal Carnot thermodynamic engine has an efficiency of 0.600.If it operates between a deep lake with a constant temperature of $294.0 \mathrm {~K}$ and a hot reservoir,what is the temperature of the hot reservoir?

What is the change in entropy of the lead when 2.0 kg of molten lead at its melting point temperature solidifies? For lead: L_V = 207 kcal/kg at 1744°C,L_F = 5.9 kcal/kg at 328°C.

An ideal Carnot engine is operated between a hot and a cold reservoir.The temperature difference between the two reservoirs is 284°C.If the efficiency of this ideal engine is 24.0%,find the temperature of the cold reservoir in degrees Celsius.