ap physics 2 thermodynamics - mcq

In the model of ideal gases, the pressure of a gas is a measure of the average impulse between the gas molecules and the walls of the container holding the gas when the molecules collide elastically with the container. The figure shows one such collision, in which a molecule's momentum is reversed in direction by the collision. In the context of the model, which of the following explain why the pressure of a gas in a container of fixed volume decreases as the temperature of the gas decreases? Select two answers.

- As gas temperature decreases, the gas molecules' average speed decreases. This means the average change in momentum for each collision is less, so the pressure throughout the gas is less. - As gas temperature decreases, the gas molecules' average speed decreases. This means the gas molecules take longer to travel between the walls of the container and collide with the walls less often, so the pressure throughout the gas is less.

An ideal gas is contained in a thermally insulated cylinder with a movable piston. The piston moves toward the bottom of the cylinder, decreasing the volume occupied by the gas. Which of the following correctly explains why the gas pressure increases? Select two answers.

- The average force exerted by the gas molecules on the cylinder walls during collisions has increased because the average speed of the gas molecules has increased. - The number of collisions per time interval of the gas molecules against the cylinder walls has increased because the gas molecules have a shorter distance to travel between collisions.

The graph shows data for pressure as a function of temperature for an ideal gas in a rigid cylinder. Based on the graph, which of the following can be concluded about the pressure in the cylinder? Select two answers.

- The pressure of the gas is zero at a temperature near −300°C. - Pressure of the gas is directly proportional to the temperature.

Two metal bars with the same length and same cross-sectional area are placed between two tanks with temperatures of 400 K and 300 K, as shown above. The thermal conductivity of the top bar is 200 W/ m ⋅ K, and that of the bottom bar is 400 W/ m ⋅ K . If the net energy transferred through the top bar in a given time interval is Q, what is the net energy transferred through the bottom bar during the same time interval?

2Q

Two blocks of steel, the first of mass 1 kg and the second of mass 2 kg, are in thermal equilibrium with a third block of aluminum of mass 2 kg that has a temperature of 400 K. What are the respective temperatures of the first and second steel blocks?

400 K and 400 K

A sheet of paper in a classroom has an area of 0.060m2 . The classroom has a volume of 300m3 and contains 1.3×104mol of air molecules at atmospheric pressure. How much force does the air exert on one side of the paper?

6000N

A student wants to conduct an experiment to determine the rate at which windows transfer energy to the outside air in the winter. The student investigates windows that are made from two parallel pieces of glass with a space in between, as shown in the figure. The student decides to investigate how the spacing between the pieces of glass affects the transfer of energy. Which additional criteria should the student use when selecting windows for the experiment? Select two answers.

C) Select windows with pieces of glass made from the same type of glass. D) Select windows with pieces of glass made from the same thickness of glass.

Students are asked to design an experiment to confirm that the pressure and volume of an ideal gas are inversely proportional. They use a cylinder containing an ideal gas that has a plunger equipped with a pressure sensor. They perform several trials, and in each trial they start with the gas at the same initial pressure and volume. The students then quickly push the plunger so that the gas achieves a different final pressure and volume. After analyzing their results, they determine that the final pressures and volumes do not follow an inversely proportional relationship. Which of the following refinements to the procedure would show the inverse proportionality between pressure and volume?

Compress the gas slowly so that the temperature remains constant.

In time t, an amount of heat Q flows through the solid door of area A and thickness d represented above. The temperatures on each side of the door are T2 and T1, respectively. Which of the following changes would be certain to decrease Q ?

Decreasing A and T2 - T1 only

A canister and the hydrogen gas it contains are at 100°C. The canister is placed in a vacuum, and the temperature of the canister and gas begins to decrease. Which of the following statements of reasoning best explains how the canister-gas system loses energy?

Energy is released from the canister as infrared radiation that can travel through the vacuum, causing a decrease in the average energy of the canister and the molecules.

Students are given a cylindrical container that has a moveable piston and contains a sample of gas. The gas can be heated, and there are blocks of known mass that can be set on top of the piston. Probes are available to measure the temperature and pressure of the gas, and a ruler is available to measure the diameter D of the container and the height H of the piston.

How does the volume of the gas depend on its temperature?

Two objects are heated to different temperatures. The objects are then placed in thermal contact with each other and insulated from their surroundings. After equilibrium is reached, which of the following must be true? I. The temperatures of the two objects are equal. II. The amount of thermal energy lost by one object equals that gained by the other object. III. The total energy of the insulated system has not changed.

I, II, and III

A student collects two data points for a sample of a gas that can be treated as ideal and is in a rigid container: T1=300K, P1=3.0kPa and T2=310K, P2=3.1kPa. Which of the following is the best conclusion about the pressure of an ideal gas at absolute zero (that is, T=0K) that can be made from this data?

No conclusion can be made, because a pattern cannot be validated based on only two data points.

A student fills balloons using an insulated helium tank with a known fixed volume V. The student fills each balloon with helium, then measures the pressure P, temperature T, and number of moles n of the remaining helium in the tank. Which of the following is the best relationship to graph to determine the value of the universal gas constant R?

P as a function of nT/V

Some students want to investigate the relationship between the pressure and volume of a gas. They take a sealed, thin-walled metal can full of air, place it in a vat of liquid nitrogen, and observe that the can collapses. Another student says that their procedure is a better demonstration of the effect of temperature on another property of the gas. Which of the following properties of the gas does the procedure best relate to temperature?

Pressure

Students design an experiment with a curved, insulated rod of an unknown thermally conducting material, as shown in the figure. The rod is 1 m long and 2 cm in diameter. One end of the rod is touching the surface of water kept at 350K by a hot plate, and the other end is just touching the surface of a well-insulated block of ice. The rod is removed from the apparatus and placed in a warm room until it reaches thermal equilibrium. Its ends are then positioned to touch the ends of an identical rod with a much colder temperature, as shown in the figure. Which of the following is the best explanation of how energy is transferred between the rods as they approach thermal equilibrium?

Quickly vibrating molecules in the warm rod collide with slowly vibrating molecules in the cold rod, and on average the slower molecules begin to vibrate faster.

A sealed cylinder with a movable piston contains N molecules of an ideal gas. The gas is initially in the state with pressure P0 and volume 3V0 shown on the graph of pressure P as a function of volume V. The gas is then taken through the two processes shown.Which of the following claims correctly describes the average force the gas exerts on the piston as the gas is taken through one of the processes?

The average force increases during process 2 because the pressure of the gas increases.

A closed system consists of two adjacent chambers containing the same ideal gas. Initially, one chamber is hot and the other chamber is cold. Which of the following best explains the change in entropy of this closed system over time?

The entropy increases over time because the process is irreversible.

Ice cubes are added to an insulated cup of hot water. As a result, the temperature of the water decreases and the ice melts. What statement best explains the change in entropy of the system, which is the combination of water and ice cubes, on a molecular level?

The entropy of the system increases, because the disorder caused by the change in state from solid to liquid water causes more disorder than liquid water cooling causes order.

Two containers, each holding a different gas, are brought into thermal contact. The gas atoms in container X have twice the mass and half the average speed of the gas atoms in container Y. Which of the following best describes the energy transfer by thermal conduction, if any, between the two containers?

There is a net energy transfer from container Y to container X.

Students perform an experiment to determine the relationship between the pressure and temperature of an ideal gas. They have a flask with a stopper through which a syringe and a pressure sensor are inserted, as shown in the figure. The flask is in a water bath whose temperature can be adjusted. There is a temperature sensor to measure the temperature of the water.The students fix the plunger in place and take measurements of temperature and pressure. They graph the data and draw a best-fit line, as shown. Which of the following is equal to the slope of the line?

nr/V