Question 1

Which of the following best describes the First Law of Thermodynamics as it applies to a closed system?

Accepted Answer

The change in internal energy of a system equals the heat added to the system minus the work done by the system: $$\Delta U = Q - W$$

Question 2

A 2 kg block is lifted vertically by 5 m. What is the change in its gravitational potential energy? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$98\ \mathrm{J}$$

Question 3

Which of the following statements about the Lennard-Jones potential $$U = \frac{A}{r$$^{12}$$} - \frac{B}{r^6$} is $$correct?

Accepted Answer

The $$\frac{A}{r$$^{12}$$}$$ term represents the repulsive part, and the $$\frac{B}{r^6$}$$ term represents the attractive part.

Question 4

A gas molecule in a container collides with the wall and bounces back. Which type of energy is primarily involved in this process?

Accepted Answer

Kinetic energy of the molecule

Question 5

Given the potential energy curve shown in the Lennard-Jones plot, at which point is the force between two atoms zero?

Accepted Answer

At $$r_0$$ where $$U is $$minimum

Question 6

Which of the following best explains why heat transfer and work are considered different processes in thermodynamics?

Accepted Answer

Heat is energy transfer due to temperature difference, while work is energy transfer due to force acting over a distance.

Question 7

A spring with spring constant $$k = 200\ \mathrm{N/m} is $$compressed by $$0.1\ \mathrm{m}. $$What is the potential energy stored in the spring?

Accepted Answer

$$2\ \mathrm{J}$$

Question 8

Which of the following is a correct statement about the direction of force relative to the potential energy curve $$U(x)$$?

Accepted Answer

The force points opposite to the slope of the potential energy curve: $$F = -\frac{dU}{dx}$$

Question 9

Two neutral atoms are brought very close together. According to the Lennard-Jones potential, what happens to the force between them as the distance decreases below $$r_0$$?

Accepted Answer

The force becomes strongly repulsive.

Question 10

A system absorbs $$150\ \mathrm{J} of $$heat and does $$40\ \mathrm{J} of $$work on the environment. What is the change in internal energy of the system?

Accepted Answer

$$110\ \mathrm{J}$$

Question 11

Which of the following best describes the difference between temperature and thermal energy?

Accepted Answer

Temperature is a measure of the average kinetic energy per molecule, while thermal energy is the total internal energy due to molecular motion and interactions.

Question 12

In the context of the First Law of Thermodynamics, which of the following real-world scenarios best illustrates the conversion of work into internal energy?

Accepted Answer

A gas being compressed rapidly in a bicycle pump, causing it to heat up.

Question 13

Which of the following is true about the force between two atoms at a distance $$r_1$$ where the Lennard-Jones potential crosses zero?

Accepted Answer

The force is attractive.

Question 14

A 0.5 kg ball is thrown vertically upward with a speed of $$10\ \mathrm{m/s}. $$What is its kinetic energy at the moment it leaves the hand?

Accepted Answer

$$25\ \mathrm{J}$$

Question 15

Which of the following best describes the energy changes when a block slides to a stop on a rough surface?

Accepted Answer

Kinetic energy is converted into internal (thermal) energy due to friction.

Question 16

If the force between two atoms is given by $$F = -\frac{dU}{dr}$$, what does a negative value of $$F$$ indicate?

Accepted Answer

The force is attractive.

Question 17

Which of the following is a correct application of the First Law of Thermodynamics to a biological system, such as a human body?

Accepted Answer

The body converts chemical energy from food into work and heat, changing its internal energy.

Internal Energy, Thermodynamics, and Potential Energy in Physics

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