Physics Unit 2 Review
The figure shows the movement of a fluid through an automobile engine and a radiator. The system is designed to prevent overheating of the engine. Which of the following claims correctly describe the energy transfer processes involved? Select two answers.
-Thermal energy is transferred out of the hot fluid in the radiator, and the resulting cooler fluid is then used to cool the engine. -The hot engine adds thermal energy to the cool fluid, which reduces the temperature of the engine and raises the temperature of the cool fluid.
A sample of an ideal gas is in a sealed cylinder with a movable piston and is initially in state A, as shown in the graph of pressure P as a function of volume V. The gas's temperature in state A is 300K. The gas can be taken from state A to state D via three separate paths, AD, ABD, or ABCD. What is the temperature of the gas in state B?
600K
A quantity of an ideal gas, initially at zero degrees Celsius, is placed in a container of unknown fixed volume. The gas is heated, and the temperature and pressure are measured, resulting in the graph shown. Which of the following quantities can be determined from a best-fit line to the data?
Absolute zero
A rigid container holds an ideal gas. A gas molecule of mass m moving at speed v collides with a container wall. The molecule's velocity is perpendicular to the wall before the collision. What type of collision occurs when the molecule strikes the wall, and what is the change in momentum of the molecule?
Collison: Elastic Change in Momentum: 2mv
A sample of an ideal gas can be taken through the four thermodynamic processes, W, X, Y, and Z, shown in the four graphs of pressure P as a function of volume V. Processes W and X occur once every second while processes Y and Z occur twice every second. Which of the following correctly ranks the energy E transferred out of the gas in a given time interval?
EY>(EW=EZ)>EX
When water boils, bubbles of water vapor form in the liquid and travel to the surface of the water. At the surface the bubbles burst, and the water vapor molecules collide with the surrounding air, which is at room temperature. Which of the following claims best describes the flow of energy between the water vapor molecules and the air molecules and the resulting change in temperature of the air and water vapor?
Energy flows into the air. The temperature of the air increases, and the temperature of the water vapor decreases.
A gas is enclosed in a container. Figure 1 shows one gas molecule moving up and to the right toward a wall of the container. The molecule collides with the wall and afterward moves up and to the left. Figure 2 shows the average force exerted by the molecule on the wall. Which of the following best shows the average force exerted on the molecule during the collision? Gravity is negligible.
Horizontal to the left
The graph shows pressure as a function of volume for a sample of an ideal gas in a cylinder. Which of the following is correct about the net work done by the gas during the cycle shown?
It is equal to the area enclosed by the cycle, because the net work is the work done by the gas during process XX minus the work done on the gas during process YY.
Oxygen molecules are in a closed container. One such molecule is traveling at 400m/s when it collides perpendicularly with the wall of the container. The mass of an oxygen molecule is 5.3×10−26 kg. The molecule can be treated as if it were a spherical particle, and the gas can be treated as ideal. What are the magnitudes of the change in the momentum and the change in the kinetic energy of the oxygen molecule due to the collision?
Momentum: 4.2X10^-23 KE: 0J
A student has a sample of gas in an insulated cylindrical container with a movable piston. The student compresses the gas by increasing the force exerted on the piston and measures the pressure and volume of the gas. The student needs to determine the work done on the gas. Which of the following describes a correct analysis of information from the graph that will determine the work?
Multiply the total change in pressure by the total change in volume. Divide the result by two. Add to this the product of the final pressure and the total change in volume.
A sample of an ideal gas is in a sealed cylinder with a movable piston and is initially in state A, as shown in the graph of pressure P as a function of volume V. The gas's temperature in state A is 300K. The gas can be taken from state A to state D via three separate paths, AD, ABD, or ABCD. For which of the paths, if any, is the change in the internal energy of the gas greatest?
None; the change in internal energy is the same for all three paths.
A sample of ideal gas is in a sealed rectangular container that has sides of different sizes. Side A has an area of 80cm2 and side B has an area of 100cm2. Which of the following correctly compares the pressure P exerted on sides A and B of the container and explains the relationship in terms of net force and molecular collisions with the sides?
PB=PA. The pressure is the same on both sides because although the average force exerted by the individual molecules as they collide with the sides is the same, the net force and area are both proportionally greater for side BB.
A student has a sample of gas with a known temperature and volume in an insulated cylinder with a piston and wants to investigate the relationship between temperature and volume. The student quickly pushes on the piston to reduce the volume a small amount and measures the new temperature and volume of the gas. This procedure is repeated to get measurements for increasingly smaller volumes of the gas. The data show that as the volume of the gas decreases, its temperature increases, which appears to contradict the ideal gas law. Which of the following modifications to the experiment would demonstrate the relationship between temperature and volume in the ideal gas law?
Perform a new experiment with hot gas that uses an object on top of the piston to keep the pressure of the gas constant while the gas is allowed to cool.
Students are given a solid rod made of an unknown material and are asked to determine the thermal conductivity k of the rod. The rod is initially at room temperature. They measure the length L and the cross-sectional area A of the rod. Which of the following procedures would provide the most reliable estimate of k ?
Place one end of the rod in a water bath at 100°C. At regular time intervals, measure the temperature at the other end of the rod and the amount of energy needed to keep the water bath at 100°C.
The graph shows pressure as a function of volume for a sample of an ideal gas that is confined in a cylinder. A moveable piston sits on top of the gas, and the piston can move vertically with negligible friction. The weight of the piston is significantly less than the force exerted by the gas on the piston during the process shown. Which of the following is true of the acceleration of the piston during the process?
The acceleration stays the same since the net force on the piston stays the same.
To launch a rocket, fuel in its engines is ignited, and the combustion produces gases at high pressure. As the combustion gases escape downward from one end of the rocket, the rocket is accelerated upward. Which of the following claims correctly describes forces in this situation?
The combustion gases are pushed out of the rocket because the pressure inside the engine is greater than the pressure outside the rocket. The rocket exerts a net downward force on the gases, which means the gases exert a net upward force on the rocket.
A student is sitting on the ground a few meters away from a campfire on a cool, windless night. The student feels noticeably warm on the side facing toward the fire, and noticeably cool on the side facing away from the fire. Which of the following models describes the primary method by which the side of the student facing toward the fire is warmed?
The fire emits electromagnetic radiation. Some of the radiation is absorbed by the student and is converted to thermal energy.
An object is placed on the moveable piston of a cylinder filled with a gas. The object exerts a downward force F on the piston that accelerates the piston downward, compressing the gas. Which of the following is a correct description of the magnitude of the upward force exerted by the piston on the object?
The force exerted by the piston on the object is equal to F.
The figure shows a horizontal metal bar with the left end in thermal contact with a constant temperature reservoir that is much hotter than the initial temperature of the bar. The reservoir-bar system is thermally isolated from the surroundings. The atoms of the metal bar are represented by the black dots. Which of the following provides the best reasoning for how the system reaches thermal equilibrium?
The hotter atoms on the left are vibrating faster than the colder atoms on the right and collide with the colder atoms, transferring kinetic energy until the bar reaches thermal equilibrium with the reservoir.
A gas is in a sealed cylinder fitted with a movable piston, as shown in the figure, so that none of the gas escapes. The cylinder and piston are made of an insulating material. The cylinder is fitted with pressure and temperature sensors, and the volume of the confined gas can be measured from markings on the side of the cylinder. The gas is initially in a state with pressure Pi, temperature Ti, and volume Vi. The piston is slowly compressed and data are recorded until the gas reaches a final state with pressure Pf, temperature Tf, and volume Vf. A graph of the pressure as a function of volume is shown, with dotted lines indicating isotherms. Which of the following claims correctly indicates the changes in the collisions between gas molecules and the cylinder wall that contribute to the change in pressure of the gas as it goes from its initial to its final state?
The volume decreases, so the number of collisions per unit time increases. The average speed of the molecules increases, so the average impulse of the collisions increases.
A room with length L, width W, and height H is filled with n moles of an ideal gas at temperature T, as represented by the figure. Which of the following indicates the magnitude and direction of the average force exerted on the gas by wall X ?
nRT/W, into the page
A container filled with gas is sealed on the top by a piston of negligible mass and area 0.005m2. The container and gas are allowed to reach thermal equilibrium with the surrounding air, and a block on top of the piston keeps the piston in place. If the pressure inside the container is 3×105Pa, what is the total downward force exerted on the piston?
1500N
Gas molecule A is moving to the right with speed v, as shown in the figure, when it collides with identical gas molecule B, which is at rest. After the collision, molecule A is moving directly toward the top of the page with the same speed v. Which of the following best represents the net force on molecule A during the collision?
Arrow pointing to the left at an angle
A gas is in a sealed cylinder fitted with a movable piston, as shown in the figure, so that none of the gas escapes. The cylinder and piston are made of an insulating material. The cylinder is fitted with pressure and temperature sensors, and the volume of the confined gas can be measured from markings on the side of the cylinder. The gas is initially in a state with pressure Pi, temperature Ti, and volume Vi. The piston is slowly compressed and data are recorded until the gas reaches a final state with pressure Pf, temperature Tf, and volume Vf. A graph of the pressure as a function of volume is shown, with dotted lines indicating isotherms. Which of the following describes the energy transfer process that the insulation prevents?
Collisions of gas molecules with the inner surface of the cylinder cause disturbances of molecules of the insulating material that travel through the cylinder, transferring energy to air molecules that hit the outer surface of the cylinder
A student watches a soap bubble drift from inside a warm room, out an open window, and into the cold air outside. The student notices that the bubble gets smaller once it is outside. Assuming no air leaks out of the bubble, what conclusion could the student reasonably draw from this observation?
If the bubble were cooled even further, there is a temperature at which the volume of the bubble approaches zero.
Two types of gas atoms are mixed in an insulated container. The atoms collide and stick together, forming a gas of a new substance. The temperature of the new gas is higher than the temperatures of either of the original gases. Suppose the speeds of two colliding atoms of the original gases are known, and the speed of the resulting new gas molecule is determined using conservation of momentum. Can this new speed be used to determine the change in kinetic energy of the two-atom system as a result of the collision?
No, because kinetic energy is lost in inelastic collisions and the kinetic energy of the new gas increases, meaning the reaction that produced the new gas must have released energy.
Which of the following describes the microscopic difference between the change in entropy of a gas during reversible processes (which are theoretical) and irreversible processes (which actually occur)?
Reversible: The number of combinations of microscopic states that can combine to create the macroscopic state of the gas remains the same. Irreversible: The number of combinations of microscopic states that can combine to create the macroscopic state of the gas increases.
The temperature of an ideal gas is held constant as its volume is slowly decreased. Which of the following claims correctly describes the cause of the increase in the force exerted by the gas on the walls of the container?
The gas molecules strike the walls more frequently.
A gas is in a sealed cylinder fitted with a movable piston, as shown in the figure, so that none of the gas escapes. The cylinder and piston are made of an insulating material. The cylinder is fitted with pressure and temperature sensors, and the volume of the confined gas can be measured from markings on the side of the cylinder. The gas is initially in a state with pressure Pi, temperature Ti, and volume Vi. The piston is slowly compressed and data are recorded until the gas reaches a final state with pressure Pf, temperature Tf, and volume Vf. A graph of the pressure as a function of volume is shown, with dotted lines indicating isotherms. Which of the following claims identifies the change in internal energy of the gas between its initial and final states and describes the corresponding changes in energy due to work and heating?
Internal energy increases. Energy is added to the gas via work and none is lost by heating.
An oxygen atom (of mass m) has a speed of 2v0 collides with another oxygen atom that has a speed of v0 in the same direction. As a result, the two atoms exert forces on each other and form an oxygen molecule. Assume that the two-atom system is completely isolated and no energy is released. Which of the following correctly predicts the resulting changes in the momentum and kinetic energy of the two-atom system as the atoms form a molecule?
The momentum does not change. The kinetic energy decreases.
A metal block with temperature 90°C is placed in a container. Water with temperature 10°C is then poured into the container. Which of the following explains how the temperature of the block changes?
The temperature of the block decreases continuously as particles in the block collide with particles in the water until the temperatures of the block and water become equal at a temperature between 10°C and 90°C.
An ideal gas is confined in a container with a moveable piston. The graph of pressure as a function of volume shows four different processes in which the gas is compressed. Which of the following correctly ranks the magnitude of the work W done on the gas in the four processes?
W2>W1>(W3=W4)
The table lists experimental data related to the conduction of energy by three slabs of metal. The slabs have identical dimensions but are made of different metals. Which of the following correctly ranks the metals' thermal conductivities k ?
k1>k2>k3
A sample of an ideal gas is contained in a cylinder with a moveable piston. The gas expands, doing work W on the piston and absorbing thermal energy Q from its surroundings. Which of the following identifies and justifies the correct form of the first law of thermodynamics during this process?
ΔU=Q−W, because thermal energy is transferred to the gas and work is done by the gas.
The figure shows a sample of an ideal gas enclosed within a cylinder that has been fitted with a movable piston. The piston and the sides of the cylinder are thermally insulated. The bottom of the cylinder is in contact with a thermal reservoir. The gas is compressed isothermally while thermal equilibrium is maintained with the reservoir. The piston, gas, and reservoir form a closed, isolated system. True statements about entropy for this reversible situation include which of the following? Select two answers.
-The entropy of the gas decreases because work is done on the gas while its temperature remains constant. -The entropy of the reservoir increases because thermal energy is transferred to it from the gas.
The figure shows an experimental setup with two thermal reservoirs connected by a uniform solid cylindrical bar. The experiment is performed twice, once with bar X and then with bar Y. The graph shows the amount of energy Q transferred through each bar as a function of time t. If there is only one difference between the experimental situations, which of the following could account for the differences in the lines on the graph for each bar? Select two answers.
-The thermal conductivity of bar X is greater than that of bar Y. -The length of bar X is less than that of bar Y.
Disk 1 of mass m is initially fixed inside a cylinder of cross-sectional area A. One end of the cylinder is closed, as shown in the figure, and the space between the closed end and disk 1 contains a gas that is maintained at gauge pressure P. Disk 1 is then released and accelerates through a distance d as it is pushed by the gas. After exiting the cylinder, disk 1 is surrounded by air of pressure P0. It then collides with and sticks to disk 2 of mass 3m that is at rest. If friction is negligible, what is the final kinetic energy of the two-disk system?
(PAd)/4
A block with mass mb sits at rest on a movable piston with mass mp that is fitted in the top of a cylindrical tank filled with a gas. When the block is removed, the piston accelerates upward. Free-body diagrams for the piston before and after the block is removed are shown above. Which of the following gives the correct expression for the acceleration of the piston at the instant after the block is removed?
(mb/mp)g
A cylinder is fitted with a low-friction, movable piston and filled with air at room temperature and atmospheric pressure, as shown in the left figure. The initial volume of the cylinder is 0.20m3. The bottom of the cylinder is placed in an ice water bath, as shown in the right figure, causing the volume to decrease to 0.15m3. The atmospheric pressure is 1.0×105Pa. What is the work done on the air inside the cylinder during this process?
5.0×10^3J
An ideal gas is sealed in a cylindrical container with an open top and a moveable piston, as shown in the figure. The piston has a mass of 10kg and a radius of 10cm. At the instant shown, the pressure of the gas in the cylinder is 105,000Pa. The free-body diagram shows the forces acting on the piston at this instant, which are the force FGas exerted by the ideal gas in the container, the force FAir exerted by the air above the piston, and the force Fg due to gravity. The magnitude of the acceleration of the piston is most nearly
5.7m/s2
In the system shown, a movable piston is initially at rest inside a cylindrical vacuum chamber. The piston has area 0.050m2 and mass 0.50kg . An explosion just above the piston produces a pressure of 60,000Pa on the piston, causing it to rapidly accelerate downward . The free-body diagram of the piston just after the explosion is shown. What is the magnitude of the piston's acceleration at this instant?
6010m/s2
An ideal gas is in a sealed cylinder with a moveable piston, as shown. In collisions between any two molecules of the gas, the linear momentum and the kinetic energy of the two-molecule system are the same before and after the collision. The gas is then heated until it reaches a certain temperature, and the heat source is removed. Which of the following claims correctly describes the linear momentum and kinetic energy in a collision between two gas molecules of the hotter gas?
Both the linear momentum and the kinetic energy have the same values before and after the collision.
A sample of an ideal gas is in a sealed cylinder with a movable piston and is initially in state A, as shown in the graph of pressure P as a function of volume V. The gas's temperature in state A is 300K. The gas can be taken from state A to state D via three separate paths, AD, ABD, or ABCD. In which process is energy transferred from the gas to the environment by heating only?
CD
Gases do not always behave ideally. Suppose one oxygen atom of a sample of gas is moving with speed v when it collides with and sticks to another oxygen atom that is momentarily at rest. Which of the following claims correctly describes the linear momentum and kinetic energy of the two-atom system after the collision compared to the linear momentum and kinetic energy before the collision?
Linear Momentum: same KE: less
A sample of gas X initially has a higher temperature than a sample of gas Y. The molecules of gas X have more mass than the molecules of gas Y. The samples are mixed together in an insulated container. Which of the following claims best describes the collisions between gas X and gas Y molecules?
Molecules of both gases will sometimes gain and sometimes lose momentum, and sometimes gain and sometimes lose kinetic energy.
Students perform an experiment to determine the number of moles in a sample of an ideal gas. The students place the sample in a container with a movable piston. A thermometer and a pressure sensor are attached to the container. The gas is initially at a temperature of 293K. The students cool the gas to 273K in an ice bath, recording the temperature and pressure at regular intervals during the process. The students are surprised to find that the pressure remains constant as the temperature decreases. How could the students refine their experiment to determine the number of moles of gas present in the sample?
Perform the same experiment with the piston held in place so that the volume is constant.
Two identical samples of helium gas are in identical sealed flasks at room temperature. One flask is just sitting in the room, and the other is inside a large, insulated vacuum container. Both flasks are opened and the samples are released, so the helium in one flask spreads throughout the room and the helium in the other flask spreads in the sealed container, as shown in the figures. Which of the following is true of the change in entropy that occurs in each case when the flasks are opened?
The entropy increases in both cases because each system is now in a more disordered state.
A gas contains two types of charged particles. Negatively charged particle X− has mass m and velocity +v0 , as shown in the figure. It collides head-on with positively charged particle Y+ that has mass 8m and velocity −v0 . Electrostatic force then holds the particles together. What is the final velocity of the two-particle system?
-7/9v
A system consists of two containers containing different liquids. The system is insulated, and no thermal energy is lost to or gained from the environment. Liquid A has a density of 800kg/m3 and an initial temperature of 60°C , while liquid B has a density of 1000kg/m3 and an initial temperature of 20°C. Which of the following statements accurately predicts what will happen once the containers are put into thermal contact? Select two answers.
-After a long time, the liquids will have the same temperature. -Thermal energy will be transferred from liquid AA to liquid BB because liquid AA has more internal energy per molecule.
Students want to investigate the inverse relationship between the pressure and volume of an ideal gas as predicted by the ideal gas law. Their plan is to use a gas-filled cylinder with a movable piston on one end and compress the piston. The students will then measure the volume and pressure of the gas when the piston is in various positions. Which of the following additions to this procedure will allow the students to observe the predicted relationship between pressure and volume? Select two answers.
-Maintain a constant gas temperature by surrounding the cylinder in a constant temperature water bath. -Ensure the piston and cylinder walls don't allow gas in or out of the cylinder.
Which of the following correctly explain why the pressure of a gas in a rigid container increases with increasing temperature? Select two answers.
-The average molecular kinetic energy increases with temperature, so the molecules exert a larger average force on the walls of the container when they collide with the walls of the container. -The average molecular speed increases with temperature, so the molecules collide with the walls of the container more frequently.
A positive gas ion with mass 1.66×10−27kg is traveling with speed 150m/s in the +x-direction when it collides head-on with a negative gas ion with mass 2.32×10−27kg traveling with speed 150m/s in the −x-direction. The ions stick together. What is the total kinetic energy of the two-ion system immediately after the collision?
1.2×10^−24J
Compressed air in a vertical cylinder with a piston of radius 0.30m is used to lift a crate. The minimum pressure of the air in the cylinder needed for the piston to lift the crate is 1.61×105N/m2, and the pressure in the room outside the piston is 1.01×105N/m2. If the mass of the piston is negligible, the weight of the crate is most nearly
1.7×10^4N F=ΔP⋅A
A gas enclosed in a cylinder has a pressure of 2.0×105Pa. The ends of the cylinder have a diameter of 0.40m and the cylinder has a height of 0.30m. The magnitude of the force exerted by the gas on the wall at one end of the cylinder is most nearly
2.5×104N F=PA=P(πr2)
An ideal gas is confined within a rigid container with a fixed lid. The container is placed on a heat source. Which of the following correctly compares the force exerted on the lid by the ideal gas and the force exerted on the ideal gas by the lid, and correctly relates the force to pressure?
The force of the ideal gas on the lid is equal to the force of the lid on the ideal gas, but the force is increasing because of the increased kinetic energy of the ideal gas, leading to an increase in pressure.
A sphere of radius R is filled with n moles of helium gas at a constant temperature T. A second sphere of radius 2R is filled with the same amount of helium gas at the same temperature. Which of the following is a reason why the pressure in the second sphere is less than that in the first sphere?
The molecules in the second sphere have to go travel a longer distance between collisions with the walls of the sphere than the molecules in the first sphere do.
A student has four square plates. The two large plates are the same size but made of materials with different thermal conductivity, and are initially at thermal equilibrium with their surroundings. The two identical small square plates are initially heated to a temperature greater than that of the surroundings. Each small plate is placed in contact with one of the large plates in the configuration shown. For each configuration, the student will measure the time it takes for the temperature to begin to rise at one or both of the labeled points. A shorter time means a higher thermal conductivity. Measurement at which of the points gives the best information for determining which material has higher thermal conductivity?
Measurement at either point A or point B, because the relative times for either point will give sufficient information.
The figure shows a cylinder that has a movable piston and contains an ideal gas initially in state 1 at room temperature. The cylinder is sealed. Blocks of known mass can be added to or removed from the top of the piston. The gas is taken through the process represented by the graph of pressure P as a function of volume V. Which of the following actions could cause the gas to go through the process represented by the graph?
Placing the cylinder on a block of ice while keeping the mass on the piston constant
The figure shows a cylinder that has a movable piston and contains an ideal gas initially in state 1 at room temperature. The cylinder is sealed. Blocks of known mass can be added to or removed from the top of the piston. The gas is taken through the process represented by the graph of pressure P as a function of volume V. Which of the following energy bar charts could represent the process as the gas is taken from state 1 to state 2, where U1 represents the initial internal energy of the N molecules of gas, Q represents the energy transferred to the gas by heating, W represents the work done on the gas, and U2 represents the final internal energy of the gas?
Above, below, above, above
When a room-temperature spoon is placed in a cold bowl of ice cream, some of the ice cream quickly melts where it comes into contact with the spoon. Which of the following is the best explanation for why the ice cream melts?
Energy is transferred to the ice cream molecules and increases their average speed, because the higher-energy molecules in the spoon are vibrating and colliding with the lower-energy molecules of the ice cream.
A cylindrical container with a movable piston contains a fixed amount of ideal gas. Initially, it is in thermal equilibrium with an ice-water bath. The diagram shows the forces exerted on the piston. The cylinder is then removed from the ice water and placed into a hot-water bath. The system slowly comes to thermal equilibrium with its surroundings. The forces exerted on the piston once the system reaches equilibrium are shown in the figure. What is the relationship among the forces exerted on the piston?
Fgas=(Fatm+mg)
A student conducts an experiment to measure the universal gas constant R using the apparatus shown. A cylinder with volume markings is filled with 0.45mol of helium gas at room temperature and pressure. The piston is connected to a lever system, as shown in Figure 1, with a pivot that is connected to a fixed support and moving hinges that allow the lever to push the rod and piston down. The student pushes on the lever and moves the piston down, as shown in Figure 2, to compress the gas as slowly and steadily as possible while the pressure, volume, and temperature of the gas are measured. The graph on the left shows pressure as a function of volume for this process. The graph on the right shows PVnT as a function of time, which should show that R is constant. The student suspects that there is a problem with the experimental apparatus that caused the variation in data between 1 and 2 atm pressure. Which of the following issues with the apparatus would most likely have caused the anomalous data?
Hinges that stick and cause uneven motion of the lever
Two gas particles collide. Particle A has mass MA, and particle B has mass MB. When they collide, they exert forces on each other as shown in the diagrams, and particle A has an acceleration with magnitude aA and particle B has an acceleration with magnitude aB. Which of the following correctly indicates the ratio aAaB and whether the accelerations are in the same or the opposite directions?
Ratio: Mb/Ma Direction: Opposite
