Question 1

Which of the following best describes the First Law of Thermodynamics?

Accepted Answer

The change in the internal energy of a system is equal to the heat added to the system minus the work done by the system.

Question 2

A gas in a piston is compressed by its surroundings, and 200 J of work is done on the gas while 100 J of heat is released by the gas. What is the change in internal energy $$\Delta U of $$the gas? (Use the University Physics sign convention: $$\Delta U = Q - W$$ where $$W is $$work done BY the system.)

Accepted Answer

$$\Delta U = -100\ \mathrm{J} - (-200\ \mathrm{J}) = 100\ \mathrm{J}$$

Question 3

Which of the following statements about internal energy $$U is $$correct?

Accepted Answer

Internal energy depends only on the current state of the system, not on how it got there.

Question 4

In Joule's paddle wheel experiment, what was demonstrated about the relationship between work and heat?

Accepted Answer

Mechanical work and heat are equivalent ways to change the internal energy of a system.

Question 5

A steam engine converts heat from burning fuel into mechanical work. According to the First Law of Thermodynamics, what happens to the energy that is not converted into work?

Accepted Answer

It increases the internal energy of the system or is lost as heat to the surroundings.

Question 6

Which equation correctly expresses the First Law of Thermodynamics for a finite process?

Accepted Answer

$$\Delta U = Q - W$$

Question 7

A cup of coffee cools down as it sits on a table. Which of the following best describes the energy changes involved?

Accepted Answer

The internal energy of the coffee decreases as heat is transferred to the surroundings.

Question 8

A gas expands in a cylinder, doing 150 J of work on the surroundings while absorbing 200 J of heat. What is the change in internal energy $$\Delta U$$?

Accepted Answer

$$\Delta U = 200\ \mathrm{J} - 150\ \mathrm{J} = 50\ \mathrm{J}$$

Question 9

Which of the following is a correct statement about the sign convention for work in the University Physics textbook?

Accepted Answer

Work is positive when done by the system (expansion), negative when done on the system (compression).

Question 10

A rock rolls down a hill and comes to rest after hitting a wall. According to the First Law of Thermodynamics, what happens to the rock's initial potential energy?

Accepted Answer

It is transformed into internal energy (disordered kinetic energy) within the rock and surroundings.

Question 11

Which of the following is NOT a correct implication of the First Law of Thermodynamics?

Accepted Answer

It is possible to create energy from nothing in a closed system.

Question 12

During a thermodynamic process, a system absorbs 300 J of heat and its internal energy increases by 100 J. How much work did the system do on its surroundings?

Accepted Answer

$$W = Q - \Delta U = 300\ \mathrm{J} - 100\ \mathrm{J} = 200\ \mathrm{J}$$

Question 13

Which of the following best describes a state variable in thermodynamics?

Accepted Answer

A property that depends only on the current state of the system, not on the path taken.

Question 14

A refrigerator removes heat from its interior and expels it to the surroundings. According to the First Law of Thermodynamics, what must be true about the work done by the refrigerator?

Accepted Answer

The refrigerator must do work to transfer heat from a colder to a hotter region.

Question 15

Which of the following real-world systems does NOT operate based on the First Law of Thermodynamics?

Accepted Answer

None; all listed systems (steam engines, rocket engines, car engines, refrigerators, living organisms) operate based on the First Law.

Question 16

If a system undergoes a cyclic process (returns to its original state), what is the net change in its internal energy $$\Delta U$$?

Accepted Answer

$$\Delta U = 0$$

Question 17

Which of the following is a correct differential form of the First Law of Thermodynamics?

Accepted Answer

$$dU = dQ - dW$$

Question 18

A gas is compressed isothermally (constant temperature) by its surroundings. Which of the following statements is true?

Accepted Answer

The work done on the gas is balanced by heat leaving the system, so $$\Delta U = 0.$$

The First Law of Thermodynamics: Energy, Heat, and Work

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