Exam 11: Using Energy

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 heat from the interior of the house?

An ideal gas undergoes an adiabatic process while doing 25 J of work. What is the change in the internal (thermal)energy of the gas?

A reversible engine takes in heat at a rate of 555 W and exhausts heat 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)?

An ideal Carnot engine has an efficiency of 83.0% and performs 4500 J of work every cycle. How much energy is discharged to the lower temperature reservoir every cycle?

An ideal gas undergoes an isothermal expansion. During this process, its entropy

Which one of the following is a true statement?

Two ideal Carnot heat engines have the same efficiency. One operates between 5.0 × 10² K and 3.0 × 10² K, and the other between 4.0 × 10² K and some lower temperature. What is the lower temperature?

A refrigerator has a performance coefficient (COP)of 1.15, and it extracts 7.95 J of heat from the cold reservoir during each cycle. (a)How much work is done on the gas in each cycle? (b)How much heat is exhausted into the hot reservoir in each cycle?

A coal-fired plant generates 600 MW of electric power. The plant uses 4.8 × 10⁶ kg of coal each day, and the heat of combustion of coal is 3.3 × 10⁷ J/kg. The steam that drives the turbines is at a temperature of 300°C, and the exhaust water is at 37°C. (a)What is the overall efficiency of the plant for generating electric power? (b)How much thermal energy is exhausted each day? (c)Using the same heat reservoirs, what is the maximum possible efficiency for a heat engine?

A certain heat engine extracts 1.30 kJ of heat from a hot temperature reservoir and discharges 0.70 kJ of heat to a cold temperature reservoir. What is the efficiency of this engine?

An ideal Carnot engine operating between a warm reservoir of unknown temperature and a cold reservoir at $1.76 \mathrm {~K}$ has an efficiency of $11.0 \%$ What is the temperature of the warm reservoir?

An ideal Carnot engine is operated as a heat pump to heat a room in the winter. The heat pump delivers heat 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 heat pump under these operating conditions is closest to

Which two temperature changes are equivalent?

A real (non-Carnot)heat engine, operating between heat reservoirs at temperatures of 450 K and 270 K, performs 3.3 kJ of net work, and rejects 8.2 kJ of heat in a single cycle. (a)What is the thermal efficiency of this heat engine? (b)What is the maximum efficiency it could possibly have?

The figure shows a pV diagram for a cycle of a heat engine for which Q_H = 59 J. What is the thermal efficiency of the engine?

A fluid in an insulated, flexible bottle is heated by a high resistance wire and expands. If $9.0 \mathrm {~kJ}$ of heat is applied to the system and it does $5.0 \mathrm {~kJ}$ of work, how much does the internal (thermal)energy of the fluid change?

A heat engine absorbs 85.6 kJ of heat each cycle and exhausts 61.8 kJ. (a)What is the efficiency of the engine? (b)How much work does it do each cycle?

An inventor tries to sell you his new heat engine that takes in 40 J of heat at 87°C on each cycle, expels 30 J at 27°C, and does 10 J of work. Would it be wise to invest in this engine? Back up your conclusion with numerical calculations.

An ideal Carnot refrigerator with a performance coefficient (COP)of 5.0 cools items inside of it to $5.0 ^ { \circ } \mathrm { C } \text {. }$ What is the high temperature needed to operate this refrigerator?

The weather outside is frightful. The temperature is -22°F. What is the corresponding temperature in the Celsius scale?