Question 1

-The thermal efficiency of a heat engine is given by:

Accepted Answer

A)    . 
B)    . 
C)    . 
D) all of the formulas above. 
E) only (a) or (b) above. 
A)    . 
B)    . 
C)    . 
D) all of the formulas above. 
E) only (a) or (b) above. E

Question 2

A petrol engine absorbs 2500 J of heat at 250$\degree$C and expels 2000 J at a temperature of 50$\degree$C. The magnitude of the change in entropy (in J/K) for the system is:

Accepted Answer

A) 6.2 
B) 4.7 
C) 1.4 
D) 10.9 
E) 3.2 
A) 6.2 
B) 4.7 
C) 1.4 
D) 10.9 
E) 3.2 A

Question 3

When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is:

Accepted Answer

A) cm ln(T2/T1) 
B) cm (T2/T1) 
C) cm (T2 - T1)/T1 
D) cm (T2 - T1)/T2 
E) cm (T2 - T1)/(T2 + T1) 
A) cm ln(T2/T1) 
B) cm (T2/T1) 
C) cm (T2 - T1)/T1 
D) cm (T2 - T1)/T2 
E) cm (T2 - T1)/(T2 + T1) A

Question 4

An 800-MW electric power plant has an efficiency of 30%. It loses its waste heat in large cooling towers. Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?

Accepted Answer

A) 1200 
B) 1900 
C) 800 
D) 560 
E) 240 
A) 1200 
B) 1900 
C) 800 
D) 560 
E) 240

Question 5

In a nuclear power plant, the reactor produces 500$\degree$C steam that is used to power the steam turbines which generate 1500 MW of electrical power. The cooling tower eliminates the waste heat at 50$\degree$C. If the efficiency of the plant were that of a Carnot engine, at what rate would waste heat be vented to the atmosphere?

Accepted Answer

The answer of In a nuclear power plant, the reactor...

Question 6

A Carnot cycle, operating as a heat engine, consists, in the order given, of:

Accepted Answer

A) an isothermal expansion, an isothermal compression, an adiabatic expansion and an adiabatic compression. 
B) an adiabatic expansion, an adiabatic compression, an isothermal expansion and an isothermal compression. 
C) an isothermal expansion, an adiabatic compression, an isothermal compression and an adiabatic expansion. 
D) an adiabatic compression, an isothermal compression, an isothermal expansion and an adiabatic expansion. 
E) an isothermal expansion, an adiabatic expansion, an isothermal compression and an adiabatic compression. 
A) an isothermal expansion, an isothermal compression, an adiabatic expansion and an adiabatic compression. 
B) an adiabatic expansion, an adiabatic compression, an isothermal expansion and an isothermal compression. 
C) an isothermal expansion, an adiabatic compression, an isothermal compression and an adiabatic expansion. 
D) an adiabatic compression, an isothermal compression, an isothermal expansion and an adiabatic expansion. 
E) an isothermal expansion, an adiabatic expansion, an isothermal compression and an adiabatic compression.

Question 7

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 kJ of heat from the cold outdoors in each cycle, the heat expelled (in kJ) to the warm indoors is:

Accepted Answer

A) 34 
B) 27 
C) 36 
D) 40 
E) 80 
A) 34 
B) 27 
C) 36 
D) 40 
E) 80

Question 8

Exactly 500 grams of ice are melted at a temperature of 0$\degree$C. (Lice = 333 J/g.) The change in entropy (in J/K) is:

Accepted Answer

A) 321 
B) 146 
C) 512 
D) 610 
E) 5230 
A) 321 
B) 146 
C) 512 
D) 610 
E) 5230

Question 9

Find the change in entropy (in J/K) when 5.00 moles of an ideal gas undergo a free expansion from an initial volume of 20 cm3 to a final volume of 100 cm3.

Accepted Answer

A) 71 
B) 52 
C) 67 
D) 191 
E) 208 
A) 71 
B) 52 
C) 67 
D) 191 
E) 208

Question 10

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is:

Accepted Answer

A) 0 K. 
B) 0$\degree$C. 
C) 0$\degree$F. 
D) 0$\degree$R. 
E) the same as the temperature of the heat source. 
A) 0 K. 
B) 0$\degree$C. 
C) 0$\degree$F. 
D) 0$\degree$R. 
E) the same as the temperature of the heat source.

Question 11

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Qc/Qh, we can calculate:

Accepted Answer

A) n, the number of moles of the ideal gas. 
B) the ratio Vc/Vh of the volumes of the ideal gas. 
C) the ratio Pc/Ph of the pressures of the ideal gas. 
D) the ratio PcVc/PhVh of the products of volumes and pressures of the ideal gas. 
E) the value of Avogadro's number. 
A) n, the number of moles of the ideal gas. 
B) the ratio Vc/Vh of the volumes of the ideal gas. 
C) the ratio Pc/Ph of the pressures of the ideal gas. 
D) the ratio PcVc/PhVh of the products of volumes and pressures of the ideal gas. 
E) the value of Avogadro's number.

Question 12

Every second at Niagara Falls, some 5000 m3 of water falls a distance of 50 m. What is the increase in entropy per second due to the falling water? (Assume a 20$\degree$C environment).

Accepted Answer

The answer of Every second at Niagara Falls, some 5000...

Question 13

What is the probability of rolling either a 7 or 11 on a single roll of a pair of dice?

Accepted Answer

A) 1/6 
B) 2/9 
C) 3/8 
D) 1/3 
E) 1/2 
A) 1/6 
B) 2/9 
C) 3/8 
D) 1/3 
E) 1/2

Question 14

Which of the following is an almost reversible process?

Accepted Answer

A) The explosion of hydrogen and oxygen to form water. 
B) Heat transfer through thick insulation. 
C) The adiabatic free expansion of a gas. 
D) A slow isothermal compression of a gas. 
E) A slow leakage of gas into an empty chamber through a small hole in a membrane. 
A) The explosion of hydrogen and oxygen to form water. 
B) Heat transfer through thick insulation. 
C) The adiabatic free expansion of a gas. 
D) A slow isothermal compression of a gas. 
E) A slow leakage of gas into an empty chamber through a small hole in a membrane.

Question 15

A company that produces pulsed gas heaters claims their efficiency is approximately 90%. If an engine operates between 250$\degree$C and 25$\degree$C, what is its maximum thermodynamic efficiency?

Accepted Answer

A) 83% 
B) 65% 
C) 43% 
D) 90% 
E) 56% 
A) 83% 
B) 65% 
C) 43% 
D) 90% 
E) 56%

Question 16

A heat engine absorbs 2500 J of heat from a hot reservoir and expels 1000 J to a cold reservoir. When it is run in reverse, with the same reservoirs, the engine pumps 2500 J of heat to the hot reservoir, requiring 1500 J of work to do so. Find the ratio of the work done by the heat engine to the work done by the pump. Is the heat engine reversible?

Accepted Answer

A) 1.0 (no) 
B) 1.0 (yes) 
C) 1.5 (yes) 
D) 1.5 (no) 
E) 2.5 (no) 
A) 1.0 (no) 
B) 1.0 (yes) 
C) 1.5 (yes) 
D) 1.5 (no) 
E) 2.5 (no)

Question 17

A lawn mower has a 6-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is:

Accepted Answer

A) 1800 J 
B) 2000 J 
C) 2200 J 
D) 2400 J 
E) 2250 J 
A) 1800 J 
B) 2000 J 
C) 2200 J 
D) 2400 J 
E) 2250 J

Question 18

All real engines are less efficient than the Carnot engine because:

Accepted Answer

A) they do not operate through the Otto cycle. 
B) they do not operate through a reversible cycle. 
C) the working substance does not maintain a constant volume through the cycle. 
D) the working substance does not maintain a constant pressure through the cycle. 
E) the working substance does not maintain a constant temperature through the cycle. 
A) they do not operate through the Otto cycle. 
B) they do not operate through a reversible cycle. 
C) the working substance does not maintain a constant volume through the cycle. 
D) the working substance does not maintain a constant pressure through the cycle. 
E) the working substance does not maintain a constant temperature through the cycle.

Question 19

The change in entropy of a mass m of a solid substance which has a latent heat of fusion L and melts at a temperature T is:

Accepted Answer

A) LT/m 
B) mL ln(T) 
C) mLT 
D) mL/T 
E) L/mT 
A) LT/m 
B) mL ln(T) 
C) mLT 
D) mL/T 
E) L/mT

Question 20

A violation of the second law of thermodynamics would occur if:

Accepted Answer

A) a ball lying on the ground started to bounce. 
B) transfer of energy by heat moved energy from an object at low temperature to an object at a higher temperature. 
C) a refrigerator heated the air in the room in which the refrigerator is located. 
D) any of the above occurred. 
E) (a) or (b) occurred, but not (c). 
A) a ball lying on the ground started to bounce. 
B) transfer of energy by heat moved energy from an object at low temperature to an object at a higher temperature. 
C) a refrigerator heated the air in the room in which the refrigerator is located. 
D) any of the above occurred. 
E) (a) or (b) occurred, but not (c).

-The thermal efficiency of a heat engine is given by:

A petrol engine absorbs 2500 J of heat at 250 $\degree$ C and expels 2000 J at a temperature of 50 $\degree$ C. The magnitude of the change in entropy (in J/K) for the system is:

When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is:

An 800-MW electric power plant has an efficiency of 30%. It loses its waste heat in large cooling towers. Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?

A Carnot cycle, operating as a heat engine, consists, in the order given, of:

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 kJ of heat from the cold outdoors in each cycle, the heat expelled (in kJ) to the warm indoors is:

Exactly 500 grams of ice are melted at a temperature of 0 $\degree$ C. (Lice = 333 J/g.) The change in entropy (in J/K) is:

Find the change in entropy (in J/K) when 5.00 moles of an ideal gas undergo a free expansion from an initial volume of 20 cm3 to a final volume of 100 cm3.

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is:

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Qc/Qh, we can calculate:

Every second at Niagara Falls, some 5000 m3 of water falls a distance of 50 m. What is the increase in entropy per second due to the falling water? (Assume a 20 $\degree$ C environment).

What is the probability of rolling either a 7 or 11 on a single roll of a pair of dice?

Which of the following is an almost reversible process?

A company that produces pulsed gas heaters claims their efficiency is approximately 90%. If an engine operates between 250 $\degree$ C and 25 $\degree$ C, what is its maximum thermodynamic efficiency?

A lawn mower has a 6-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is:

All real engines are less efficient than the Carnot engine because:

The change in entropy of a mass m of a solid substance which has a latent heat of fusion L and melts at a temperature T is:

A violation of the second law of thermodynamics would occur if:

Physics and Measurement

Motion in One Dimension

Motion in Two Dimensions

Forces and Newtons Laws

Further Applications of Newtons Laws

Work, Force and Energy

Conservation of Energy

Linear Momentum and Collisions

Rotational Motion

Energy and Momentum in Rotating Systems

Gravity

Special Relativity

Fluid Statics

Fluid Dynamics

Solids

Oscillatory Motion

Wave Motion

Superposition and Interference

Heat and Temperature

Energy Transfer Processes and Thermodynamics

The Kinetic Theory of Gases

Filters

Exam 22: The Second Law of Thermodynamics, Heat Engines and Entropy

-The thermal efficiency of a heat engine is given by:

A petrol engine absorbs 2500 J of heat at 250 °\degree° C and expels 2000 J at a temperature of 50 °\degree° C. The magnitude of the change in entropy (in J/K) for the system is:

When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is:

An 800-MW electric power plant has an efficiency of 30%. It loses its waste heat in large cooling towers. Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?

A Carnot cycle, operating as a heat engine, consists, in the order given, of:

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 kJ of heat from the cold outdoors in each cycle, the heat expelled (in kJ) to the warm indoors is:

Exactly 500 grams of ice are melted at a temperature of 0 °\degree° C. (Lice = 333 J/g.) The change in entropy (in J/K) is:

Find the change in entropy (in J/K) when 5.00 moles of an ideal gas undergo a free expansion from an initial volume of 20 cm3 to a final volume of 100 cm3.

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is:

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Qc/Qh, we can calculate:

Every second at Niagara Falls, some 5000 m3 of water falls a distance of 50 m. What is the increase in entropy per second due to the falling water? (Assume a 20 °\degree° C environment).

What is the probability of rolling either a 7 or 11 on a single roll of a pair of dice?

Which of the following is an almost reversible process?

A company that produces pulsed gas heaters claims their efficiency is approximately 90%. If an engine operates between 250 °\degree° C and 25 °\degree° C, what is its maximum thermodynamic efficiency?

A lawn mower has a 6-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is:

All real engines are less efficient than the Carnot engine because:

The change in entropy of a mass m of a solid substance which has a latent heat of fusion L and melts at a temperature T is:

A violation of the second law of thermodynamics would occur if:

Physics and Measurement

Motion in One Dimension

Motion in Two Dimensions

Forces and Newtons Laws

Further Applications of Newtons Laws

Work, Force and Energy

Conservation of Energy

Linear Momentum and Collisions

Rotational Motion

Energy and Momentum in Rotating Systems

Gravity

Special Relativity

Fluid Statics

Fluid Dynamics

Solids

Oscillatory Motion

Wave Motion

Superposition and Interference

Heat and Temperature

Energy Transfer Processes and Thermodynamics

The Kinetic Theory of Gases

Filters

A petrol engine absorbs 2500 J of heat at 250 $\degree$ C and expels 2000 J at a temperature of 50 $\degree$ C. The magnitude of the change in entropy (in J/K) for the system is:

Exactly 500 grams of ice are melted at a temperature of 0 $\degree$ C. (Lice = 333 J/g.) The change in entropy (in J/K) is:

Every second at Niagara Falls, some 5000 m3 of water falls a distance of 50 m. What is the increase in entropy per second due to the falling water? (Assume a 20 $\degree$ C environment).

A company that produces pulsed gas heaters claims their efficiency is approximately 90%. If an engine operates between 250 $\degree$ C and 25 $\degree$ C, what is its maximum thermodynamic efficiency?