Problem 1:
The timekeeper of quartz clock is a tiny quartz tuning fork. Suppose that the clock is running a little slow (i.e., it is counting off the seconds more slowly than it should). What change to the tuning fork could fix this problem, so that the clock keeps correct time?
(A) Decrease the amplitude of motion of the two tips of the tuning fork. [13.7% picked]
(B) Increase the amplitude of motion of the two tips of the tuning fork. [7.7% picked]
(C) Add a little mass to the two tips of the tuning fork. [13.2% picked]
(D) Remove a little mass from the two tips of the tuning fork. [65.4% picked]
Answer: (D) Remove a little mass from the two tips of the tuning fork. [65.4% picked]
Why: TBA
Problem 2:
One of the components of an air conditioner is its evaporator. Inside that evaporator, the unit's working fluid transforms from a liquid to a gas. While this transformation is occurring, what else is happening around the evaporator?
(A) Heat is flowing into the evaporator from the surrounding air. [43.6% picked]
(B) Heat is flowing out of the evaporator into the surrounding air. [44.9% picked]
(C) The evaporator is doing work on the surrounding air. [10.7% picked]
(D) The surrounding air is doing work on the evaporator. [0.9% picked]
Answer: (A) Heat is flowing into the evaporator from the surrounding air. [43.6% picked]
Why: TBA
Problem 3:
A window air conditioner normally operates between the indoor air and the outdoor air. Suppose you place the unit on a table in the middle of the room, plug it in, and turn it on. What will happen to the average temperature of the room as the unit operates?
(A) The room's average temperature will remain unchanged. [24.8% picked]
(B) The room's average temperature will decrease. [0.9% picked]
(C) The room's average temperature can increase, decrease, or remain constant, depending on what the room's initial temperature was. [5.1% picked]
(D) The room's average temperature will increase. [69.2% picked]
Answer: (D) The room's average temperature will increase. [69.2% picked]
Why: TBA
Problem 4:
A spaceship in deep empty space is moving toward a remote space station at a constant velocity. To maintain that constant velocity, what forward thrust (forward propulsive force) must the spaceship's rocket engine obtain from its plume of exhaust?
(A) The engine must obtain a thrust force equal to the spaceship's weight. [18.0% picked]
(B) The engine must obtain a thrust force equal to the spaceship's velocity divided by its mass. [7.7% picked]
(C) The engine must obtain a thrust force equal to the spaceship's velocity divided by its acceleration. [2.6% picked]
(D) The engine must obtain zero thrust force. [71.7% picked]
Answer: (D) The engine must obtain zero thrust force. [71.7% picked]
Why: TBA
Problem 5:
You are standing in front of an open freezer at the grocery store, trying to decide which flavor of ice cream to buy. Even though you aren't touching the freezer or the cold air pouring out of it toward the floor, you still feel surprisingly cold. Why is the freezer making you feel cold?
(A) The freezer is radiating much less thermal energy at you than you are radiating at it, so there is a net transfer of heat from you to the freezer. [52.1% picked]
(B) It's all in your head. You are not actually exchanging any thermal energy with the freezer. [0.0% picked]
(C) The freezer is radiating cold at you, cancelling your thermal energy and making you feel cold. [5.1% picked]
(D) You are radiating thermal energy at the freezer, but the freezer is not radiating thermal energy at you. You are therefore losing thermal energy. [42.7% picked]
Answer: (A) The freezer is radiating much less thermal energy at you than you are radiating at it, so there is a net transfer of heat from you to the freezer. [52.1% picked]
Why: TBA
Problem 6:
After a storm covers the ground with snow, the weather turns warm and the snow begins to melt. You are in a restaurant, with a glass of ice and water in front of you. The temperature outside is 50 °F (10 °C) and the temperature inside is 68 °F (20 °C). Compare the temperature of the melting snow outside to the ice water in your glass inside.
(A) The temperature of your ice water is greater than the temperature of the melting snow. [9.4% picked]
(B) The temperature of your ice water is less than the temperature of the melting snow. [9.8% picked]
(C) Their relative temperatures depend on the fractions of ice and water in your glass. [6.8% picked]
(D) Their temperatures are the same. [73.9% picked]
Answer: (D) Their temperatures are the same. [73.9% picked]
Why: TBA
Problem 7:
A gong is a stiff metal disk that emits sound when struck by a mallet. The pitch of the gong's fundamental vibrational mode is present in its sound and that pitch doesn't change as the gong's loudness decreases. The gong's other tones, however, give it a brash sound similar to that of a drum or cymbal rather than the more melodic sound a string or wind instrument. That's because the gong is a vibrating surface and it
(A) behaves as harmonic oscillators. [3.4% picked]
(B) has overtones with pitches that are not integer multiples of its fundamental frequency. [81.2% picked]
(C) has overtones with pitches that are integer multiples of its fundamental frequency. [7.7% picked]
(D) does not behave as harmonic oscillators. [7.7% picked]
Answer: (B) has overtones with pitches that are not integer multiples of its fundamental frequency. [81.2% picked]
Why: TBA
Problem 8:
You are at the seashore, watching a seabird float on the water far from shore. As a large wave travels across the water toward shore, it encounters the bird. What effect does the passing wave have on the bird?
(A) The bird moves toward shore at the same speed as the wave's crests. [3.8% picked]
(B) The bird moves toward shore at half the speed of the wave's crests. [2.1% picked]
(C) The bird moves toward shore at a speed proportional to the amplitude of the wave's crests. [15.4% picked]
(D) The bird moves in a circle as the wave passes and is left approximately where it started. [78.6% picked]
Answer: (D) The bird moves in a circle as the wave passes and is left approximately where it started. [78.6% picked]
Why: TBA
Problem 9:
You are riding a cable car in San Francisco and are moving uphill at constant velocity. What overall force is the cable car exerting on you? [Neglect any effects due to the air.]
(A) The car's force on you is upward and equal in amount to your weight. [78.2% picked]
(B) The car's force on you is uphill (toward your destination) and greater in amount than your weight. [3.8% picked]
(C) The car's force on you is uphill (toward your destination) and less in amount than your weight. [1.3% picked]
(D) The car's force on you is uphill (toward your destination) and equal in amount to your weight. [16.7% picked]
Answer: (A) The car's force on you is upward and equal in amount to your weight. [78.2% picked]
Why: TBA
Problem 10:
What is the primary reason why increasing the concentration of carbon dioxide in the Earth's atmosphere leads to an increase in the average temperature near the Earth's surface?
(A) The added carbon dioxide reduces the air's ability to undergo convection so that it cannot convey heat as well. [9.4% picked]
(B) The added carbon dioxide reduces the air's thermal conductivity so that it becomes a better thermal insulator. [44.2% picked]
(C) The added carbon dioxide is hotter than the atmosphere and therefore increases the average air temperature. [6.9% picked]
(D) The added carbon dioxide darkens (blackens) the atmosphere for the infrared light associated with room-temperature thermal radiation. [39.5% picked]
Answer: (D) The added carbon dioxide darkens (blackens) the atmosphere for the infrared light associated with room-temperature thermal radiation. [39.5% picked]
Why: TBA
Problem 11:
In January 1903, Wilbur Wright made a discovery that revolutionized airplane propellers and made powered flight possible. His realization was that each blade of a propeller is
(A) a wing that rotates about a pivot. [53.8% picked]
(B) an inclined plane that rotates about a pivot. [15.4% picked]
(C) a ramp that rotates about a pivot. [2.1% picked]
(D) a paddle that rotates about a pivot. [28.6% picked]
Answer: (A) a wing that rotates about a pivot. [53.8% picked]
Why: TBA
Problem 12:
The three nonflammable objects in your hand are identical except that one is black, one is white, and one is shiny. You place them in a roaring fire and soon they have the same high temperature: 1800 °C. They remain solid. Which one is glowing most brightly with visible light?
(A) The object that originally appeared white. [3.0% picked]
(B) They are all glowing with equal brightness. [0.9% picked]
(C) The object that originally appeared silver. [2.1% picked]
(D) The object that originally appeared black. [94.0% picked]
Answer: (D) The object that originally appeared black. [94.0% picked]
Why: TBA
Problem 13:
You are pulling a wagon forward on a level sidewalk and the wagon is experiencing no other horizontal force. As you exert your forward force on the wagon, the wagon exerts a backward force on you. When do those two forces cancel so that the wagon does not accelerate?
(A) When you and the wagon have equal masses. [0.9% picked]
(B) When you and the wagon have equal velocities. [2.1% picked]
(C) When those two forces are equal in amount but opposite in direction so that they sum to zero. [53.8% picked]
(D) They never cancel because they act on different objects. [43.2% picked]
Answer: (D) They never cancel because they act on different objects. [43.2% picked]
Why: TBA
Problem 14:
Why does water boil at a lower temperature in the Rocky Mountains than it does in Charlottesville?
(A) The lower atmospheric pressure in the Rocky Mountains allows steam bubbles to avoid collapse at lower temperatures. [71.8% picked]
(B) Steam bubbles float less easily in the low-density Rocky Mountain air and that makes boiling easier. [6.4% picked]
(C) The smaller air density in the Rocky Mountains is a better match for the density of steam bubbles. [2.1% picked]
(D) Steam bubbles float more easily in the low-density Rocky Mountain air and that makes boiling easier. [19.7% picked]
Answer: (A) The lower atmospheric pressure in the Rocky Mountains allows steam bubbles to avoid collapse at lower temperatures. [71.8% picked]
Why: TBA
Problem 15:
A yardstick (or meter-stick) is a long metal rectangle of uniform thickness. When the yardstick is vibrating in is fundamental vibrational mode, it bows in alternating directions along its length (see image) with a frequency of 2 Hz (2 cycles per second). If you cut the yardstick in half along its length (see image), the fundamental vibrational mode of each half-yardstick will have what frequency?
(A) 8 Hz [3.0% picked]
(B) 4 Hz [58.5% picked]
(C) 2 Hz [28.6% picked]
(D) 1 Hz [9.8% picked]
Answer: (C) 2 Hz [28.6% picked]
Why: TBA
Problem 16:
An airplane in flight gradually turns toward the right. What force does it use to change its velocity toward the right?
(A) The plane uses its rudder to pivot its nose toward the right and the plane then heads in the direction its nose is pointing. [8.1% picked]
(B) The plane uses its rudder to pivot its nose toward the right so that its propellers or jet engines push it toward the right. [3.4% picked]
(C) The plane tilts its left wing higher than its right wing so that the wings' lift forces are partly directed toward the right. [43.2% picked]
(D) The plane tilts its left wing higher than its right wing so that the wings experience drag forces. Those drag forces slow the plane's forward motion and enhance its rightward motion. [45.3% picked]
Answer: (C) The plane tilts its left wing higher than its right wing so that the wings' lift forces are partly directed toward the right. [43.2% picked]
Why: TBA
Problem 17:
When you play in water waves at the seashore, you can often outrun those wave. Tsunamis, the giant water waves created by earthquakes and other cataclysmic events, travel at race-car speeds across the ocean. Why do these waves have such different speeds?
(A) The speed of a gravity wave on water's surface increases with its total energy. High-energy waves, like a tsunami, travel much faster than the low-energy waves you normally play in at the beach. [26.9% picked]
(B) A tsunami affects the air as well as the water, so it travels much faster than the gentle waves you normally play in at the beach. [1.7% picked]
(C) The speed of a gravity wave on water's surface increases with its wavelength. Long-wavelength waves, like a tsunami, travel much faster than the short-wavelength waves you normally play in at the beach. [49.1% picked]
(D) The speed of a gravity wave on water's surface increases with its amplitude. Huge-amplitude waves, like a tsunami, travel much faster than the small-amplitude waves you normally play in at the beach. [22.2% picked]
Answer: (C) The speed of a gravity wave on water's surface increases with its wavelength. Long-wavelength waves, like a tsunami, travel much faster than the short-wavelength waves you normally play in at the beach. [49.1% picked]
Why: TBA
Problem 18:
A toy electric train is traveling around a circular toy track at a constant speed. In which direction is the train accelerating?
(A) The train is accelerating away from the center of the circular track. [0.9% picked]
(B) The train is accelerating forward, in the direction tangent to the circle. [0.9% picked]
(C) The train is not accelerating. [7.3% picked]
(D) The train is accelerating toward the center of the circular track. [91.0% picked]
Answer: (D) The train is accelerating toward the center of the circular track. [91.0% picked]
Why: TBA
Problem 19:
A squirrel runs past and two dogs simultaneously leap horizontally off the porch to give chase. The tan dog weighs twice as much as the red dog, but the red dog's horizontal starting velocity was twice that of the tan dog. When the dogs land on the level ground below the porch,
(A) the red dog lands before than the tan dog. [1.3% picked]
(B) the tan dog lands before the red dog. [0.9% picked]
(C) they land at the same time, but red dog lands considerably farther from the porch than does the tan dog. [94.0% picked]
(D) they land at the same time and at the same distance from the porch. [3.8% picked]
Answer: (C) they land at the same time, but red dog lands considerably farther from the porch than does the tan dog. [94.0% picked]
Why: TBA
Problem 20:
On a hot summer day, your home's air conditioner is maintaining the indoor air temperature at 72 °F. If the hot outdoor air becomes even hotter, how will that temperature increase affect the amount of electric energy the air conditioner consumes while pumping 1 joule of heat from the indoor air to the outdoor air?
(A) Whether the amount of electric energy consumed will increase, decrease, or remain unchanged depends on the home's thermal insulation. [4.3% picked]
(B) The amount of electric energy consumed will decrease. [7.3% picked]
(C) The amount of electric energy consumed will increase. [85.9% picked]
(D) The amount of electric energy consumed will remain unchanged. [2.6% picked]
Answer: (C) The amount of electric energy consumed will increase. [85.9% picked]
Why: TBA
Problem 21:
You are pulling a toboggan (a snow sled) full of friend forward across level snow. The toboggan is traveling at a constant horizontal velocity. Compare the forward force you exert on the toboggan to the backward force the snow exerts on the toboggan.
(A) Your forward force on the toboggan is somewhat smaller in amount than the snow's backward force on the toboggan. [1.3% picked]
(B) The snow exerts zero force on the toboggan. [3.8% picked]
(C) Those two forces are equal in amount but opposite in direction. [91.0% picked]
(D) Your forward force on the toboggan is somewhat larger in amount than the snow's backward force on the toboggan. [3.8% picked]
Answer: (C) Those two forces are equal in amount but opposite in direction. [91.0% picked]
Why: TBA
Problem 22:
When a ray of sunlight passes through an otherwise darkened room, it illuminates tiny dust particles in the air. If the room's air were perfectly calm, no wind at all, the dust particles would
(A) move slowly downward at constant velocity. [32.1% picked]
(B) be motionless, like the air surrounding them. [28.2% picked]
(C) accelerate downward at the acceleration due to gravity (9.8 meters per second squared). [35.9% picked]
(D) move slowly upward at constant velocity. [3.8% picked]
Answer: (A) move slowly downward at constant velocity. [32.1% picked]
Why: TBA
Problem 23:
You are inflating a shiny plastic balloon with helium. The balloon starts as a thin, flat bag but it gradually gets thicker as it fills. At first, the thin plastic balloon doesn't float. But as you keep adding helium to the balloon and it gets thicker, it eventually begins floating because
(A) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases more rapidly and the buoyant force eventually exceeds the balloon's weight. [87.2% picked]
(B) the upward buoyant force on a balloon full of helium is larger than the buoyant force on an identical balloon full of air. [1.7% picked]
(C) the helium-filled balloon's weight decreases as you put more lightweight helium particles inside it and eventually it becomes weightless. [3.8% picked]
(D) the average pressure of the helium-filled balloon increases as it fills and its pressure eventually becomes greater than that of the air it displaces. [7.3% picked]
Answer: (A) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases more rapidly and the buoyant force eventually exceeds the balloon's weight. [87.2% picked]
Why: TBA
Problem 24:
An acoustic guitar has an elaborately shaped wooden box in addition to its strings. What is the primary purpose of that box?
(A) To assist the strings in producing sound because the strings alone produce almost zero sound. [42.7% picked]
(B) To increase the amplitude of the strings' vibrations so that the guitar sounds louder. [27.4% picked]
(C) To provide the restoring forces that make the strings harmonic oscillators. [9.0% picked]
(D) To reflect sound produced by the strings back toward the listeners. [20.9% picked]
Answer: (A) To assist the strings in producing sound because the strings alone produce almost zero sound. [42.7% picked]
Why: TBA
Problem 25:
Why must an automobile engine (an internal combustion engine that burns gasoline) release a large amount of thermal energy into the environment, rather than converting all of that thermal energy into work?
(A) Some of the thermal energy must be converted into entropy. [3.8% picked]
(B) Converting all the thermal energy into work would violate the Law of Conservation of Energy. [23.9% picked]
(C) The engine experiences sliding friction, which wastes energy. If there were no friction, the engine could convert all the thermal energy into work. [6.4% picked]
(D) Converting all the thermal energy into work would violate the Law of Entropy. [65.8% picked]
Answer: (D) Converting all the thermal energy into work would violate the Law of Entropy. [65.8% picked]
Why: TBA
Problem 26:
A spare bicycle wheel accidently falls off a shelf and rolls all the way across the warehouse before finally falling over. That wheel cannot remain upright when it is stationary, so why does it stay upright so long when it is rolling?
(A) The rolling wheel has a rotational mass and that rotational mass cannot change while the wheel is moving. [3.0% picked]
(B) When the wheel is rolling forward, it has forward momentum and it cannot tip over until its momentum has decreased to zero. [3.9% picked]
(C) Effects related to angular momentum cause the wheel to steer automatically whenever it starts to tip so that it returns itself to its unstable equilibrium. [73.0% picked]
(D) The rolling wheel has angular momentum and the wheel cannot tip over until its angular momentum has decreased to zero. [20.2% picked]
Answer: (C) Effects related to angular momentum cause the wheel to steer automatically whenever it starts to tip so that it returns itself to its unstable equilibrium. [73.0% picked]
Why: TBA
Problem 27:
The timekeeping pendulum of a grandfather clock has been adjusted so that the clock keeps perfect time here in Charlottesville. If that clock is moved carefully to top of the Blue Ridge Mountains, how will the clock behave?
(A) The pendulum's period will be slightly longer than when it was in Charlottesville and the clock will run slow. [56.4% picked]
(B) The pendulum's period will be the same as when it was in Charlottesville and the clock will keep perfect time. [21.4% picked]
(C) The pendulum's period will be slightly shorter than when it was in Charlottesville and the clock will run fast. [15.0% picked]
(D) The pendulum's period will be the same as when it was in Charlottesville, but the clock will run fast. [7.3% picked]
Answer: (A) The pendulum's period will be slightly longer than when it was in Charlottesville and the clock will run slow. [56.4% picked]
Why: TBA
Problem 28:
During the power stroke of an internal combustion engine, the hot burned gas pushes the piston out of the cylinder. What are happening to the pressure, density, and temperature of the burned gas during the power stroke?
(A) The density and temperature of the gas are decreasing, but the pressure of the gas remains constant. [3.0% picked]
(B) The pressure and temperature of the gas are decreasing, but the density of the gas remains constant. [7.3% picked]
(C) The pressure, density, and temperature of the gas are all decreasing. [85.9% picked]
(D) The pressure and density of the gas are decreasing, but the temperature of the gas remains constant. [3.8% picked]
Answer: (C) The pressure, density, and temperature of the gas are all decreasing. [85.9% picked]
Why: TBA
Problem 29:
You are visiting a playground with a variety of swings and other toys. You notice that a girl on one swing completes each full cycle of motion in much less time than a boy on another swing. The girl has a much shorter period of oscillation than the boy because
(A) the girl is much heavier than the boy. [0.9% picked]
(B) the girl is riding on a much shorter swing than the boy is riding. [97.0% picked]
(C) the girl is much lighter than the boy. [2.1% picked]
(D) the girl is riding on a much taller swing than the boy is riding. [0.0% picked]
Answer: (B) the girl is riding on a much shorter swing than the boy is riding. [97.0% picked]
Why: TBA
Problem 30:
A microwave oven can heat water in a glass container to a temperature several degree above water's normal boiling temperature. That water is superheated (or overheated). How can this superheating occur?
(A) Uniform heating by the microwaves and the smooth glass surface do not trigger bubble formation, so the water does not begin to boil despite being hot enough to boil. [71.4% picked]
(B) Glass is a poor thermal conductor, so it does not convey heat to the water fast enough to make the water boil. [12.0% picked]
(C) Microwaves do not add thermal energy to the water, so the water does not have the thermal energy it needs to boil despite being hot enough to boil. [12.4% picked]
(D) Glass is transparent, so it does not provide the thermal radiation needed to make water boil. [4.3% picked]
Answer: (A) Uniform heating by the microwaves and the smooth glass surface do not trigger bubble formation, so the water does not begin to boil despite being hot enough to boil. [71.4% picked]
Why: TBA
Problem 31:
When wood burns in air, the water and carbon dioxide molecules that form as the result of combustion reactions have
(A) less chemical momentum than the original wood and air molecules. [2.1% picked]
(B) more chemical momentum than the original wood and air molecules. [0.4% picked]
(C) less chemical potential energy than the original wood and air molecules. [95.3% picked]
(D) more chemical potential energy than the original wood and air molecules. [2.1% picked]
Answer: (C) less chemical potential energy than the original wood and air molecules. [95.3% picked]
Why: TBA
Problem 32:
Because of bad planning during the design and construction of a high-rise apartment building, all 50 floors of the building receive their water from a single pipe. That pipe is fed from a water tank located on the building's roof. On opening day, residents on various floors begin taking showers and have different experiences. They quickly discover that the total ordered energy per liter in the spraying water is (neglecting any effects of viscosity and friction)
(A) the same on all floors, but the speed of the spraying water is greater on higher floors. [2.1% picked]
(B) greater on higher floors. [0.4% picked]
(C) smaller on higher floors [1.3% picked]
(D) the same on all floors, but the speed of the spraying water is smaller on higher floors. [96.2% picked]
Answer: (D) the same on all floors, but the speed of the spraying water is smaller on higher floors. [96.2% picked]
Why: TBA
Problem 33:
You are designing a chair for a museum. While your chair will be a work of art, it must also be practical and it mustn't tip over easily. To ensure that it stays upright, you design it so that its
(A) angular velocity always remains constant if you tip it. [3.0% picked]
(B) center of gravity always rises if you tip it. [80.8% picked]
(C) velocity always remains constant if you tip it. [0.0% picked]
(D) center of gravity always descends if you tip it. [16.2% picked]
Answer: (B) center of gravity always rises if you tip it. [80.8% picked]
Why: TBA
Problem 34:
When water flowing steadily through a garden hose flows around a bend in that hose, its pressure changes. The water pressure
(A) decreases near the inside of the bend and increases near the outside of the bend. [96.6% picked]
(B) decreases near the inside of the bend and decreases near the outside of the bend. [0.0% picked]
(C) increases near the inside of the bend and decreases near the outside of the bend. [3.0% picked]
(D) increases near the inside of the bend and increases near the outside of the bend. [0.4% picked]
Answer: (A) decreases near the inside of the bend and increases near the outside of the bend. [96.6% picked]
Why: TBA
Problem 35:
A lighter person and a heavier person bungee-jump simultaneously from a bridge, side by side. They are attached to the level bridge by identical elastic cords. After a few thrilling seconds, they are both bouncing gently up and down. Which of the following correctly describes the periods of their bouncing motions and their equilibrium heights (altitudes) above the ground?
(A) The heavier person has the shorter period and the higher equilibrium height. [0.9% picked]
(B) The lighter person has the longer period and the higher equilibrium height. [6.0% picked]
(C) The lighter person has the shorter period and the higher equilibrium height. [66.7% picked]
(D) The heavier person has the longer period and the higher equilibrium height. [26.5% picked]
Answer: (C) The lighter person has the shorter period and the higher equilibrium height. [66.7% picked]
Why: TBA
Problem 36:
You are camping in the wilderness on a bitter cold day and you want to insulate your tent as effectively as possible. All you have on hand are two huge containers of popcorn, one full of popped corn and one full of unpopped corn. The corn kernels are all chemically identical, but the popped corn kernels are filled with tiny air bubbles. Which corn should you surround yourself with inside the tent to experience the best thermal insulation?
(A) The popped corn because it has a lower density than unpopped corn and low-density materials are better insulators than high-density materials. [15.4% picked]
(B) The popped corn because its trapped air provides excellent insulation. [76.9% picked]
(C) The unpopped corn because it is heavier than the unpopped corn and heavier materials are better insulators than lighter materials. [0.9% picked]
(D) The unpopped corn because it has a higher density than the popped corn and high-density materials are better insulators than low-density materials. [6.8% picked]
Answer: (B) The popped corn because its trapped air provides excellent insulation. [76.9% picked]
Why: TBA
Problem 37:
Your home's climate-control system has carefully adjusted the indoor air's temperature and humidity so that they differ from those of the outdoor air. A visitor enters and leaves the front door of your home open. What happens to the entropy of the universe because of having the door open?
(A) The universe's entropy decreases. [10.3% picked]
(B) The universe's entropy remains unchanged because entropy is a conserved physical quantity. [5.1% picked]
(C) The universe's entropy remains unchanged because of the Law of Entropy. [20.5% picked]
(D) The universe's entropy increases. [64.1% picked]
Answer: (D) The universe's entropy increases. [64.1% picked]
Why: TBA
Problem 38:
As you observe the Atlantic Ocean from a beach in eastern Virginia, you notice that the water's average level varies up and down rhythmically with about a 12-hour cycle: from high tide (maximum height) to low tide (minimum height) and back to high tide. What is the primarily cause of this cycle of tides?
(A) The Sun's thermal radiation. [0.0% picked]
(B) The Atlantic Ocean's fundamental vibrational mode. [3.4% picked]
(C) The Earth's gravity. [2.6% picked]
(D) The moon's gravity. [94.0% picked]
Answer: (D) The moon's gravity. [94.0% picked]
Why: TBA
Problem 39:
A building is being demolished and the workers are using two wrecking balls to do the job. Those wrecking balls are giant pendulums hanging from tall cranes and they're identical except that one ball is twice as heavy as the other. The balls are pulled away from equilibrium equal distances and then released from rest. They swing through equilibrium and collide violently with the building's wall. Compare their momentums, velocities, and kinetic energies as they swing through equilibrium.
(A) The two balls had equal velocities, momentums, and kinetic energies. [24.4% picked]
(B) The lighter ball had twice the velocity of the heavier ball, but the heavier ball had twice the momentum and twice the kinetic energy of the lighter ball. [9.4% picked]
(C) The heavier ball had twice the velocity, twice the momentum, and twice the kinetic energy of the lighter ball. [6.8% picked]
(D) They had equal velocities, but the heavier ball had twice the momentum and twice the kinetic energy of the lighter ball. [59.4% picked]
Answer: (D) They had equal velocities, but the heavier ball had twice the momentum and twice the kinetic energy of the lighter ball. [59.4% picked]
Why: TBA
Problem 40:
If you reach into steam (gaseous water) at a temperature of 212 °F (100 °C), your skin heats up much more quickly than if you reach into air at a temperature of 212 °F (100 °C). Why?
(A) The steam condenses on your skin, thereby releasing its latent heat of evaporation. [94.9% picked]
(B) Steam is a better conductor of heat than air. [3.8% picked]
(C) Steam has a smaller density than air, so its heat capacity is greater than that of air. [0.0% picked]
(D) Steam is able to undergo convection much more rapidly than air. [1.3% picked]
Answer: (A) The steam condenses on your skin, thereby releasing its latent heat of evaporation. [94.9% picked]
Why: TBA
Problem 41:
Two glass bottles, one blue and one green, contain only liquid water and water vapor. The liquid and gas are in phase equilibrium, but the water vapor in the blue bottle has a significantly lower density than the water vapor in the green bottle. What else is different about the two bottles?
(A) The blue bottle has a higher temperature and a lower internal pressure than does the green bottle. [20.5% picked]
(B) The blue bottle has a higher temperature and a higher internal pressure than does the green bottle. [45.3% picked]
(C) The blue bottle has a lower temperature and a lower internal pressure than does the green bottle. [26.5% picked]
(D) The blue bottle has a lower temperature and a higher internal pressure than does the green bottle. [7.7% picked]
Answer: (C) The blue bottle has a lower temperature and a lower internal pressure than does the green bottle. [26.5% picked]
Why: TBA
Problem 42:
If you blow across the top of a half-full bottle of water, you can produce a clear tone. If you drink some of the water and try this again, the frequency of the sound produced will
(A) be smaller than before your drink. [85.5% picked]
(B) be the same as before your drink. [1.3% picked]
(C) be greater than before your drink. [13.2% picked]
(D) be smaller or greater than before your drink, depending on how much water you drank. [0.0% picked]
Answer: (A) be smaller than before your drink. [85.5% picked]
Why: TBA
Problem 43:
You are preparing to plant some seeds in a flowerpot. You have a clay pot, some dry soil, and a pitcher of cold water. Which of the following actions would increase the total entropy of these 3 items: combining the water and soil, heating the water to room temperature, and/or accidently breaking the clay pot?
(A) Any of those 3 actions would increase the total entropy. [66.7% picked]
(B) Only heating the water and/or combining the water and soil would increase the total entropy. [20.5% picked]
(C) Only heating the water would increase the total entropy. [11.1% picked]
(D) Only breaking the clay pot would increase the total entropy. [1.7% picked]
Answer: (A) Any of those 3 actions would increase the total entropy. [66.7% picked]
Why: TBA
Problem 44:
During the winter, your home is heated by a heat pump. When the heat pump is consuming 1000 watts of electric power, how much thermal power is it delivering to the air in your home?
(A) Slightly less than 1000 watts of thermal power because sliding friction wastes some of the energy. [5.1% picked]
(B) Significantly more than 1000 watts of thermal power. [91.0% picked]
(C) Exactly 1000 watts of thermal power because of the Law of Conservation of Energy. [3.0% picked]
(D) Exactly 1000 watts of thermal power because of the Law of Entropy. [0.9% picked]
Answer: (B) Significantly more than 1000 watts of thermal power. [91.0% picked]
Why: TBA
Problem 45:
Your coffee has cooled off and you decide to heat it the hard way: you stir the coffee vigorously for 10 minutes. The coffee does become slightly hotter. What causes this rise in temperature?
(A) You do work on the coffee as you stir it and viscous effects turn that work into thermal energy. [100.0% picked]
(B) You are making the coffee move as though it were boiling, so that it becomes hotter. [0.0% picked]
(C) You are forcing convection to occur so that heat flows more rapidly from the cup to the coffee. [0.0% picked]
(D) You are encouraging the conduction of heat from the cup to the coffee. [0.0% picked]
Answer: (A) You do work on the coffee as you stir it and viscous effects turn that work into thermal energy. [100.0% picked]
Why: TBA
Problem 46:
How does ice form on the freezing compartment of a simple refrigerator (a typical dorm refrigerator), even when all you do is open and close the refrigerator door occasionally?
(A) Water vapor from the air deposits directly as solid ice on that compartment's cold surface. [34.2% picked]
(B) Liquid nitrogen forms on the freezing compartment's cold surface and that liquid freezes into ice. [0.4% picked]
(C) Water leaks out of the freezing compartment's cooling system and freezes into ice on the compartment's cold surface. [3.4% picked]
(D) Water vapor from the air condenses as liquid water and that liquid water then freeze into ice on the compartment's cold surface. [62.0% picked]
Answer: (A) Water vapor from the air deposits directly as solid ice on that compartment's cold surface. [34.2% picked]
Why: TBA
Problem 47:
A soccer ball that is moving forward through calm air experiences the backward force of pressure drag. Doubling the ball's forward velocity would have what effect on that pressure drag force? [Assume no change in the cross sectional area of the ball's turbulent wake.]
(A) The pressure drag force would increase by about a factor of 4. [21.4% picked]
(B) The pressure drag force would increase by about a factor of 2. [40.6% picked]
(C) The pressure drag force would increase by about a factor of 8. [6.0% picked]
(D) The pressure drag force would remain about the same. [32.1% picked]
Answer: (A) The pressure drag force would increase by about a factor of 4. [21.4% picked]
Why: TBA
Problem 48:
An airplane is in level flight. The air stream that encounters the underside of the airplane's wing bends downward, away from the wing's bottom surface. How do the pressure and speed of the air near the wing's bottom surface compare to their values far from the wing?
(A) Air near the bottom of the wing has lower pressure and lower speed. [1.7% picked]
(B) Air near the bottom of the wing has lower pressure and higher speed. [22.6% picked]
(C) Air near the bottom of the wing has higher pressure and lower speed. [65.8% picked]
(D) Air near the bottom of the wing has higher pressure and higher speed. [9.8% picked]
Answer: (C) Air near the bottom of the wing has higher pressure and lower speed. [65.8% picked]
Why: TBA
Problem 49:
The fundamental vibrational mode of a violin's A string has a frequency of 440 Hz (440 cycles per second). When you pluck that string with your finger, the vibrating string can cause the violin to produce sounds with which frequencies?
(A) 440 Hz, 330 Hz, 220, Hz, and so on. [3.0% picked]
(B) 440 Hz, 550 Hz, 660 Hz, and so on. [3.0% picked]
(C) 440 Hz, 220 Hz, 110 Hz, and so on. [12.0% picked]
(D) 440 Hz, 880 Hz, 1320 Hz, and so on. [82.1% picked]
Answer: (D) 440 Hz, 880 Hz, 1320 Hz, and so on. [82.1% picked]
Why: TBA
Problem 50:
Two metal cooking pots are identical except that one is made of aluminum and one is made of stainless steel. Why does the aluminum pot provide more uniform cooking when placed on a stovetop burner than does the stainless steel pot?
(A) Aluminum reflects thermal radiation much better than stainless steel. [36.3% picked]
(B) Aluminum emits thermal radiation much better than stainless steel. [7.3% picked]
(C) Stainless steel has a much greater thermal conductivity than aluminum. [5.1% picked]
(D) Aluminum has a much greater thermal conductivity than stainless steel. [51.3% picked]
Answer: (D) Aluminum has a much greater thermal conductivity than stainless steel. [51.3% picked]
Why: TBA
Problem 51:
When you push your warm hand against a cold, immovable granite wall, what energy does your hand transfer to that wall?
(A) Your hand transfers only ordered energy to the wall. [1.7% picked]
(B) Your hand transfers only thermal energy to the wall. [68.4% picked]
(C) Your hand transfers both thermal energy and ordered energy to the wall. [20.5% picked]
(D) Your hand does not transfer energy to the wall. [9.4% picked]
Answer: (B) Your hand transfers only thermal energy to the wall. [68.4% picked]
Why: TBA
Problem 52:
A diesel engine has no sparkplugs. What provides the high temperatures needed to ignite the fuel in a diesel engine?
(A) When the diesel engine's piston hits the end of the cylinder, the impact produces sparks that ignite the fuel. [12.0% picked]
(B) When the diesel engine's fuel mixes with air, they react spontaneously at room temperature and that reaction heats the fuel so quickly that it ignites. [6.8% picked]
(C) When the diesel engine compresses air to high density, it does work on the air and the air's temperature rises dramatically. [73.1% picked]
(D) When the diesel engine slides its piston into the cylinder, sliding friction causes the temperature of the metal to increase dramatically. [8.1% picked]
Answer: (C) When the diesel engine compresses air to high density, it does work on the air and the air's temperature rises dramatically. [73.1% picked]
Why: TBA
Problem 53:
You throw a tennis ball to friend located on the other side of a level field. When the ball is at peak height, about half way across the field, what forward force is the ball experiencing? [Neglect effects due to the air.]
(A) No forward force. [93.6% picked]
(B) A forward force equal to its momentum. [4.3% picked]
(C) A forward force equal to half its velocity. [0.4% picked]
(D) A forward force equal to its velocity. [1.7% picked]
Answer: (A) No forward force. [93.6% picked]
Why: TBA
Problem 54:
You are riding a roller coaster with a loop-the-loop and are currently upside-down at the top of the loop. You are pressed tightly into your seat, even though that seat is above you (as viewed by a person on the ground). Which of the following correctly describes your motion?
(A) Your velocity is constant and directed horizontally. [3.4% picked]
(B) Your velocity is constant and directed slightly downward (toward the Earth). [0.9% picked]
(C) Your acceleration is downward (toward the Earth) and greater than the acceleration due to gravity. [81.2% picked]
(D) Your acceleration is downward (toward the Earth) and less than the acceleration due to gravity. [14.5% picked]
Answer: (C) Your acceleration is downward (toward the Earth) and greater than the acceleration due to gravity. [81.2% picked]
Why: TBA
Problem 55:
Sunlight carries heat from the Sun to the Earth. The Sun's surface temperature is about 6000 K and the Earth's surface temperature is about 300 K. A solar cell exposed to sunlight provides electric energy, an ordered form of energy. What is the maximum fraction of sunlight's thermal energy that a solar cell can convert continuously into electric energy?
(A) Somewhat more than 100%. [6.0% picked]
(B) Somewhat less than 100%. [63.5% picked]
(C) Exactly 100%. [21.0% picked]
(D) 0%. [9.4% picked]
Answer: (B) Somewhat less than 100%. [63.5% picked]
Why: TBA
Problem 56:
A car has driven off the road into a snowdrift and you are trying to pull the car out. You tie one sleeve of an old sweater to your car and the other sleeve of the sweater to the stuck car. As you drive forward, the sweater stretches and breaks. The stuck car never moved at all. Stretching and breaking the sweater took energy, but where did that energy come from?
(A) The energy came from the stuck car. [1.7% picked]
(B) The energy came the sweater's chemical potential energy. [0.9% picked]
(C) The energy came from your car. [96.6% picked]
(D) The energy came half from your car and half from the stuck car. [0.9% picked]
Answer: (C) The energy came from your car. [96.6% picked]
Why: TBA
Problem 57:
You are looking at two different photographs of the same perfectly isolated system. Each photo shows a room with a small plastic bucket on the floor. In one photo, the bucket is full of water and the room air is dry. In the other photo, the bucket is empty and the room air is moist. Compare those two situations.
(A) The total entropy of the moist-air/empty-bucket situation is greater than the total entropy of the dry-air/full-bucket situation. [91.9% picked]
(B) The total entropy of the moist-air/empty-bucket situation is less than the total entropy of the dry-air/full-bucket situation. [3.8% picked]
(C) The total energy of the moist-air/empty-bucket situation is greater than the total energy of the dry-air/full-bucket situation. [4.3% picked]
(D) The total energy of the moist-air/empty-bucket situation is less than the total energy of the dry-air/full-bucket situation. [0.0% picked]
Answer: (A) The total entropy of the moist-air/empty-bucket situation is greater than the total entropy of the dry-air/full-bucket situation. [91.9% picked]
Why: TBA
Problem 58:
You are pushing a child on a swing. You exert a forward force of 10 newtons on the child as the child moves away from you. The child exerts a backward force on you of
(A) zero. [3.8% picked]
(B) 10 newtons. [88.9% picked]
(C) less than 10 newtons. [5.1% picked]
(D) greater than 10 newtons. [2.1% picked]
Answer: (B) 10 newtons. [88.9% picked]
Why: TBA
Problem 59:
To win a prize at the fair, you must toss a basketball into a rigid fruit basket and have the ball remain in that basket. The basket is tipped toward you and nailed immovably to the wall. Its lower lip has just enough uphill slope to keep a stationary ball from rolling out. Each time you throw the ball into the basket, the ball bounces and rolls onto the floor. The conserved quantity that the basketball is unable to get rid of in order to stay in the basket is
(A) kinetic energy. [7.7% picked]
(B) momentum. [13.7% picked]
(C) potential energy. [1.3% picked]
(D) energy. [77.4% picked]
Answer: (D) energy. [77.4% picked]
Why: TBA
Problem 60:
You are eating outside on a hot summer day and an ice cube in your glass of ice water is gradually disappearing. Which of the following describes the situation near the surface of that ice?
(A) Water molecules in the ice are vanishing entirely and an equal number of water molecules are appearing in the liquid water. [0.9% picked]
(B) Water molecules are leaving the ice for the liquid water, but water molecules are not leaving the liquid water for the ice. [23.5% picked]
(C) Water molecules in the ice are dissociating into hydrogen and oxygen and those chemicals are reassembling into liquid water. [2.1% picked]
(D) Water molecules are leaving the ice for the liquid water more often than water molecules are leaving the liquid water for the ice. [73.5% picked]
Answer: (D) Water molecules are leaving the ice for the liquid water more often than water molecules are leaving the liquid water for the ice. [73.5% picked]
Why: TBA