Problem 1:
You are trying to win a prize at the state fair by knocking a massive can off a shelf. You have a choice of 4 different objects to throw at the can, each with a mass of 1 kg. With which of the following objects are you most likely to win?
(A) A soft bean bag. [8.3% picked]
(B) A stiff bouncy ball. [71.9% picked]
(C) A soft bouncy ball. [7.9% picked]
(D) A stiff bean bag. [11.8% picked]
Answer: (B) A stiff bouncy ball. [71.9% picked]
Why: 
Video Discussion
Problem 2:
On a windless day, a pitcher throws a baseball toward home plate without any significant spin. After the ball has passed through the air, in which direction is the air moving on average?
(A) The air is moving upward. [0.9% picked]
(B) The air is moving toward home plate. [65.4% picked]
(C) The air is moving away from home plate. [21.1% picked]
(D) The air is moving downward. [12.7% picked]
Answer: (B) The air is moving toward home plate. [65.4% picked]
Why: Video Discussion
Problem 3:
When a cylinder in an automobile's engine is going through the power stroke, the hot burned gas is pushing the piston out of the cylinder. As the piston moves out of the cylinder, the burned gas does work on the piston and
(A) the pressure of the burned gas remains constant while the temperature of the burned gas decreases. [6.6% picked]
(B) the pressure and temperature of the burned gas both remain constant. [3.9% picked]
(C) the pressure and temperature of the burned gas both decrease. [79.8% picked]
(D) the pressure of the burned gas decreases while the temperature of the burned gas remains constant. [9.6% picked]
Answer: (C) the pressure and temperature of the burned gas both decrease. [79.8% picked]
Why: Video Discussion
Problem 4:
To save the earth from an asteroid impact years in the future, engineers land an explosive on the asteroid and blow it to bits. Just before the detonation, the asteroid was heading directly toward mars and just after detonation, the largest piece of asteroid is heading directly toward the sun. Just after the detonation, the total momentum of all the asteroid pieces points
(A) directly away from mars. [5.3% picked]
(B) directly toward the sun. [5.7% picked]
(C) in a direction between the sun and mars. [4.4% picked]
(D) directly toward mars. [84.6% picked]
Answer: (D) directly toward mars. [84.6% picked]
Why: Video Discussion
Problem 5:
An automobile's internal combustion engine burns a mixture of fuel and air in its cylinders. It is impossible for this engine to convert all of the chemical potential energy of the fuel and air mixture into mechanical work because burning that mixture increases its
(A) energy. [14.9% picked]
(B) momentum. [0.0% picked]
(C) pressure. [10.1% picked]
(D) entropy. [75.0% picked]
Answer: (D) entropy. [75.0% picked]
Why: Video Discussion
Problem 6:
Your grandfather clock uses a pendulum as its timekeeper. At home, that clock keeps perfect time. When you move the clock to your dorm room, where the earth's gravity is slightly weaker than at home, the clock
(A) runs a little slow (causing you to be late for classes). [64.5% picked]
(B) continues to keep perfect time because the period of a pendulum depends only on its mass and not on the strength of gravity. [6.1% picked]
(C) continues to keep perfect time because the period of a pendulum depends only on its length and not on the strength of gravity. [14.5% picked]
(D) runs a little fast (causing you to be early for classes). [14.5% picked]
Answer: (A) runs a little slow (causing you to be late for classes). [64.5% picked]
Why: Video Discussion
Problem 7:
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. [1.3% picked]
(B) less chemical potential energy than the original wood and air molecules. [90.8% picked]
(C) more chemical potential energy than the original wood and air molecules. [6.6% picked]
(D) more chemical momentum than the original wood and air molecules. [1.3% picked]
Answer: (B) less chemical potential energy than the original wood and air molecules. [90.8% picked]
Why: Video Discussion
Problem 8:
You are trying to set the world's record for drinking water through the tallest drinking straw. You only need to drink one drop of water, so speed doesn't matter. What could you do to have the best chance of setting this record?
(A) Go to the highest altitude available, preferably at the top of a tall mountain. [7.9% picked]
(B) Go to the lowest altitude available, preferably sea level or below. [82.0% picked]
(C) Use the widest drinking straw you can fit in your mouth. [3.5% picked]
(D) Use the narrowest drinking straw you can find. [6.6% picked]
Answer: (B) Go to the lowest altitude available, preferably sea level or below. [82.0% picked]
Why: Video Discussion
Problem 9:
A volleyball falls onto the ocean, where it is affected by waves traveling on the ocean's surface. If a steady pattern of wave crests is heading north at 4 mph (4 miles per hour) on a windless day, how will the floating volleyball move as it encounters this wave pattern?
(A) The volleyball will move up and down, and travel northward at 4 mph. [7.9% picked]
(B) The volleyball will move in a circle, and travel northward at 2 mph. [5.7% picked]
(C) The volleyball will move in a circle, but make no average progress in any direction. [80.3% picked]
(D) The volleyball will move up and down, and travel northward at 2 mph. [6.1% picked]
Answer: (C) The volleyball will move in a circle, but make no average progress in any direction. [80.3% picked]
Why: Video Discussion
Problem 10:
Your glass of water has one cube of ice floating at the water's surface. Part of the cube is above the water. Olive oil is less dense than water. When you pour a layer of chilled olive oil onto the water's surface, the ice cube
(A) floats at the same height so that the same amount of the cube is above the water as before. [6.1% picked]
(B) moves downward so that less of the cube is above the water. [15.8% picked]
(C) sinks to the bottom of the water. [0.0% picked]
(D) moves upward so that more of the cube is above the water. [78.1% picked]
Answer: (D) moves upward so that more of the cube is above the water. [78.1% picked]
Why: Video Discussion
Problem 11:
The characteristic of a harmonic oscillator that makes it especially suitable for use as a timekeeper in a clock is that
(A) its energy is constant, regardless of its amplitude (extent of motion). [2.2% picked]
(B) its amplitude (extent of motion) is constant, regardless of its total energy. [6.1% picked]
(C) its period of oscillation does not depend on its amplitude (extent of motion). [87.3% picked]
(D) its momentum is constant throughout its oscillation. [4.4% picked]
Answer: (C) its period of oscillation does not depend on its amplitude (extent of motion). [87.3% picked]
Why: Video Discussion
Problem 12:
You are swinging a bucket full of water around you in a big horizontal circle at a constant speed. You are at the center of its circular path. The net force on the bucket points directly
(A) toward you. [91.7% picked]
(B) along the bucket's velocity (along its direction of travel). [2.2% picked]
(C) away from you. [3.9% picked]
(D) downward. [2.2% picked]
Answer: (A) toward you. [91.7% picked]
Why: Video Discussion
Problem 13:
You are flying a kite on a long string and the kite hovers motionless in the sky as the wind blows past it. The kite is high up to your east and you are pulling the kite string downward and westward. In which direction is the kite pushing on the air that passes it?
(A) Downward and westward. [69.7% picked]
(B) Upward and eastward. [14.5% picked]
(C) Upward and westward. [3.5% picked]
(D) Downward and eastward. [12.3% picked]
Answer: (A) Downward and westward. [69.7% picked]
Why: Video Discussion
Problem 14:
You are using a hand-powered pump to add air to a bicycle tire. As you pump air quickly into the tire,
(A) the pressure of the air in the tire increases, but the density and temperature of the air remain unchanged. [3.5% picked]
(B) the pressure, density, and temperature of the air in the tire increase. [62.7% picked]
(C) the pressure and temperature of the air in the tire increase, but the density of the air remains unchanged. [20.6% picked]
(D) the pressure and density of the air in the tire increase, but the temperature of the air remains unchanged. [12.3% picked]
Answer: (B) the pressure, density, and temperature of the air in the tire increase. [62.7% picked]
Why: Video Discussion
Problem 15:
Suppose it's a hot summer day, but the air in your room is much colder than the outdoor air. If you remove 1 J of thermal energy from the cold room air and add that 1 J of thermal energy to the hot outdoor air, without doing anything else at all, what happens to the total entropy (disorder) of world?
(A) It decreases. [33.8% picked]
(B) It remains constant because you add as much entropy to the outdoor air as you remove from the indoor air. [12.7% picked]
(C) It increases. [48.7% picked]
(D) It remains constant because entropy is conserved. [4.8% picked]
Answer: (A) It decreases. [33.8% picked]
Why: Video Discussion
Problem 16:
You're eating lunch outdoors on a hot day and half the ice in your glass of water has melted since you started eating. How has the temperature of the water in your glass changed over that period?
(A) The temperature of the water has increased by 8 °F. [0.9% picked]
(B) The temperature of the water has increased by 4 °F. [2.6% picked]
(C) The temperature of the water has increased by 2 °F. [4.4% picked]
(D) The temperature of the water has remained constant. [92.1% picked]
Answer: (D) The temperature of the water has remained constant. [92.1% picked]
Why: Video Discussion
Problem 17:
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) velocity always remains constant if you tip it. [0.0% picked]
(B) center of gravity always rises if you tip it. [84.2% picked]
(C) angular velocity always remains constant if you tip it. [1.8% picked]
(D) center of gravity always descends if you tip it. [14.0% picked]
Answer: (B) center of gravity always rises if you tip it. [84.2% picked]
Why: Video Discussion
Problem 18:
When water flows around a bend in a garden hose, the water pressure
(A) increases near the inside of the curve and increases near the outside of the curve. [0.9% picked]
(B) decreases near the inside of the curve and decreases near the outside of the curve. [0.0% picked]
(C) increases near the inside of the curve and decreases near the outside of the curve. [12.7% picked]
(D) decreases near the inside of the curve and increases near the outside of the curve. [86.4% picked]
Answer: (D) decreases near the inside of the curve and increases near the outside of the curve. [86.4% picked]
Why: Video Discussion
Problem 19:
You watch from the ground as a crane lifts a large bucket of cement upward to a construction project. The bucket and cement are moving straight upward at constant velocity. As the crane's cable lifts the bucket, the cable is
(A) not doing work on the bucket, but the bucket is doing work on the cement it contains. [0.4% picked]
(B) doing work on the bucket and the bucket is doing work on the cement it contains. [90.4% picked]
(C) not doing work on the bucket or the cement it contains. [3.9% picked]
(D) doing work on the bucket, but the bucket is not doing work on the cement it contains. [5.3% picked]
Answer: (B) doing work on the bucket and the bucket is doing work on the cement it contains. [90.4% picked]
Why: Video Discussion
Problem 20:
A rocket designed to put a satellite in orbit around the earth has two main tasks. First, it must lift the satellite above earth's atmosphere to eliminate air resistance. Second, it must
(A) push upward on the satellite with a force that balances the satellite's downward weight so that the satellite can coast at constant velocity. [4.4% picked]
(B) give the satellite such a large sideways acceleration that the satellite's apparent weight is zero. [2.2% picked]
(C) give the satellite such a large horizontal speed that the falling satellite arcs endlessly around the earth rather than descending to the ground. [92.5% picked]
(D) give the satellite such a large upward vertical speed that the falling satellite cannot descend to the ground. [0.9% picked]
Answer: (C) give the satellite such a large horizontal speed that the falling satellite arcs endlessly around the earth rather than descending to the ground. [92.5% picked]
Why: Video Discussion
Problem 21:
You're drinking a cup of hot coffee in an airplane at 35,000 feet. Suddenly the airplane pressurization system fails and the cabin's air pressure decreases abruptly. The coffee begins to boil because its temperature
(A) has suddenly decreased. [2.2% picked]
(B) hasn't changed but the air bubbles inside it have suddenly expanded. [11.4% picked]
(C) has suddenly increased. [3.1% picked]
(D) hasn't changed but bubbles of pure steam are now stable inside it. [83.3% picked]
Answer: (D) hasn't changed but bubbles of pure steam are now stable inside it. [83.3% picked]
Why: Video Discussion
Problem 22:
An airplane is cruising at constant velocity, 30,000 feet in the air. Which of the following correctly describes the situation above the airplane's wing?
(A) The airstream over the wing is bending downward, toward the wing, so the pressure just above the wing must be greater than the local atmospheric pressure. [4.8% picked]
(B) The airstream over the wing is traveling straight ahead, so the pressure just above the wing must equal the local atmospheric pressure. [0.4% picked]
(C) The airstream over the wing is bending downward, toward the wing, so the pressure just above the wing must be less than the local atmospheric pressure. [72.8% picked]
(D) The airstream over the wing is bending upward, away from the wing, so the pressure just above the wing must be less than the local atmospheric pressure. [21.9% picked]
Answer: (C) The airstream over the wing is bending downward, toward the wing, so the pressure just above the wing must be less than the local atmospheric pressure. [72.8% picked]
Why: Video Discussion
Problem 23:
Even though your Thanksgiving dinner consists of a tofu turkey, you discover that it contains a wishbone. You and your cousin decide to break the wishbone; the one with the large half gets their wish. Your cousin holds one end of the wishbone motionless as you pull the other end toward you rapidly. The wishbone snaps and you're left holding only a tiny fragment. Better luck next time! Breaking the wishbone required energy and that energy was provided by
(A) neither of you. It was instead provided by chemical potential energy in the wishbone itself. [0.4% picked]
(B) your cousin. [5.3% picked]
(C) you. [89.5% picked]
(D) both you and your cousin. [4.8% picked]
Answer: (C) you. [89.5% picked]
Why: Video Discussion
Problem 24:
The chemical bond that causes two oxygen atoms to cling together as an oxygen molecules is
(A) a deficit of energy—the work needed to separate those two atoms from one another. [77.6% picked]
(B) a myth; the two atoms only think that they are bound to one another. [0.9% picked]
(C) an attractive force that the two atoms exert on one another when they are at their equilibrium separation. [18.9% picked]
(D) a repulsive force that the two atoms exert on one another when they are at their equilibrium separation. [2.6% picked]
Answer: (A) a deficit of energy—the work needed to separate those two atoms from one another. [77.6% picked]
Why: Video Discussion
Problem 25:
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 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 smaller on higher floors. [89.9% picked]
(B) the same on all floors, but the speed of the spraying water is greater on higher floors. [4.4% picked]
(C) greater on higher floors. [1.8% picked]
(D) smaller on higher floors. [3.9% picked]
Answer: (A) the same on all floors, but the speed of the spraying water is smaller on higher floors. [89.9% picked]
Why: Video Discussion
Problem 26:
Two identical rooms at identical temperatures contain identical collections of atoms. In one room that collection consists of moist air and an empty bowl and in the other room that collection consists of dry air and a bowl full of water. Which of the two rooms has the greater entropy (disorder)?
(A) The room containing moist air and an empty bowl has the greater entropy. [89.9% picked]
(B) The two rooms have equal entropies because they contain identical collections of atoms. [1.8% picked]
(C) The two rooms have equal entropies because they have identical temperatures. [3.1% picked]
(D) The room containing dry air and the full bowl has the greater entropy. [5.3% picked]
Answer: (A) The room containing moist air and an empty bowl has the greater entropy. [89.9% picked]
Why: Video Discussion
Problem 27:
Ice cubes gradually shrink in a frost-free freezer because
(A) water molecules go directly from solid ice to gaseous water vapor. [89.0% picked]
(B) the ice melts periodically and some of it evaporates before it can refreeze. [10.5% picked]
(C) the ice melts periodically and some of it drips into the bottom of the freezer. [0.4% picked]
(D) the freezer gremlins like to carve their initials on the ice cubes. [0.0% picked]
Answer: (A) water molecules go directly from solid ice to gaseous water vapor. [89.0% picked]
Why: Video Discussion
Problem 28:
Which of the following is a harmonic oscillator?
(A) A mass with a stable equilibrium that experiences a restoring force that is independent of its displacement from equilibrium. [15.8% picked]
(B) A mass with a stable equilibrium that experiences a restoring force that is proportional to its displacement from equilibrium. [82.5% picked]
(C) A mass with an unstable equilibrium that accelerates in the direction opposite its velocity. [0.4% picked]
(D) A mass with an unstable equilibrium that accelerates at constant velocity near that equilibrium. [0.9% picked]
Answer: (B) A mass with a stable equilibrium that experiences a restoring force that is proportional to its displacement from equilibrium. [82.5% picked]
Why: Video Discussion
Problem 29:
A silver flute produces a tone as the flautist blows across a hole near the end of the flute. What is vibrating to produce this tone?
(A) A column of air inside the flute is vibrating along its length. [94.7% picked]
(B) The silver body of the flute is vibrating as a single arc in which its middle moves opposite its two ends. [0.9% picked]
(C) The silver body of the flute is vibrating along its length. [1.3% picked]
(D) The silver body of the flute is vibrating as a single arc in which its middle moves back and forth while its ends remain motionless. [3.1% picked]
Answer: (A) A column of air inside the flute is vibrating along its length. [94.7% picked]
Why: Video Discussion
Problem 30:
You add a teaspoon of salt to a glass of pure water. The salt initially sits at the bottom of the water, but it slowly dissolves so that eventually you have a glass of salt water. Which has more entropy: the glass of pure water with salt sitting at its bottom or the glass of salt water?
(A) They have the same entropy because entropy is conserved. [3.9% picked]
(B) They have the same entropy because water's entropy is independent of its purity. [5.7% picked]
(C) The glass of pure water with salt at its bottom has more entropy. [8.3% picked]
(D) The glass of salt water has more entropy. [82.0% picked]
Answer: (D) The glass of salt water has more entropy. [82.0% picked]
Why: Video Discussion
Problem 31:
You wake up one very cold winter morning to find the grass outside covered with frost. How did this ice form on the grass?
(A) Water that normally evaporates from warm grass as water vapor instead evaporated as ice from the cold grass. [11.4% picked]
(B) Water molecules from the moist air landed on the cold grass more frequently than they left the grass, and there was a net accumulation of water molecules as ice. [86.0% picked]
(C) Heat from the warmer air became ice as it flowed to the colder grass [0.9% picked]
(D) Heat from the colder air became ice as it flowed to the warmer grass [1.8% picked]
Answer: (B) Water molecules from the moist air landed on the cold grass more frequently than they left the grass, and there was a net accumulation of water molecules as ice. [86.0% picked]
Why: Video Discussion
Problem 32:
The ocean tides are caused primarily by
(A) the moon's gravity distorting the earth's oceans. [94.3% picked]
(B) the cycle of temperature variations that occur over the course of each day. [0.4% picked]
(C) the centripetal acceleration of the earth's oceans as the earth rotates on its axis. [0.9% picked]
(D) the earth's oceans experiencing sympathetic vibration in response to the earth's rotation. [3.9% picked]
Answer: (A) the moon's gravity distorting the earth's oceans. [94.3% picked]
Why: Video Discussion
Problem 33:
You are visiting a playground and 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 motion (time between cycles) than the boy because
(A) the girl is much heavier than the boy. [3.5% picked]
(B) the girl is riding on a much shorter swing than the boy is riding. [87.7% picked]
(C) the girl is riding on a much taller swing than the boy is riding. [1.3% picked]
(D) the girl is much lighter than the boy. [7.5% picked]
Answer: (B) the girl is riding on a much shorter swing than the boy is riding. [87.7% picked]
Why: Video Discussion
Problem 34:
Two toy cars roll off a level table side-by-side at the same time and in the same direction. The cars soon hit the level floor below the table. The cars have identical weights, but the violet car was traveling twice as fast as the yellow car when they left the table. In this situation,
(A) the violet car hits the floor much sooner than the yellow car, but the violet car hits considerably farther from the table than the yellow car. [3.5% picked]
(B) the yellow car hits the floor much sooner than the violet car, but the violet car hits considerably farther from the table than the yellow car. [0.9% picked]
(C) the two cars hit the floor at approximately the same time, but the violet car hits considerably farther from the table than the yellow car. [92.1% picked]
(D) the two cars hit the floor at approximately the same time and the same distance from the table. [3.1% picked]
Answer: (C) the two cars hit the floor at approximately the same time, but the violet car hits considerably farther from the table than the yellow car. [92.1% picked]
Why: Video Discussion
Problem 35:
Compared to an ordinary surface wave on the ocean, a tsunami has a much longer wavelength and therefore
(A) travels much slower and has much higher pressure at the surface of the water. [23.2% picked]
(B) travels much slower and has much lower pressure at the surface of the water. [6.1% picked]
(C) travels much faster and involves water that is much deeper into the ocean. [63.6% picked]
(D) travels much faster and has its adjacent crests spaced much closer together. [7.0% picked]
Answer: (C) travels much faster and involves water that is much deeper into the ocean. [63.6% picked]
Why: Video Discussion
Problem 36:
The first kind of perpetual motion machine provides an inexhaustible supply of mechanical work (or the equivalent of work), but consumes nothing at all from its environment, not even heat. An example would be a black box that consumes nothing yet provides electricity forever. This form of perpetual motion machine is impossible because it
(A) violates the law of thermal equilibrium. [5.7% picked]
(B) violates the law of conservation of momentum. [0.0% picked]
(C) violates the law of conservation of energy. [76.3% picked]
(D) violates the law of entropy. [18.0% picked]
Answer: (C) violates the law of conservation of energy. [76.3% picked]
Why: TBA
Problem 37:
It's just below freezing outside and your walkway has a layer of slippery ice on it. Which of the following substances will cause that ice to melt if you sprinkle it on the ice?
(A) Salt, sugar, and sand. [19.7% picked]
(B) Salt, sugar, but not sand. [31.1% picked]
(C) Salt, sand, but not sugar. [29.4% picked]
(D) Salt, but not sand or sugar. [19.7% picked]
Answer: (B) Salt, sugar, but not sand. [31.1% picked]
Why: TBA
Problem 38:
When a liquid flows through a collection of stationary obstacles, its flow can be smooth and laminar, or it can be swirling and turbulent. The liquid's flow is more likely to become turbulent if you increase its
(A) viscosity. [3.5% picked]
(B) pressure. [4.8% picked]
(C) transparency. [0.9% picked]
(D) speed. [90.8% picked]
Answer: (D) speed. [90.8% picked]
Why: TBA
Problem 39:
You are eating at an outdoor restaurant on a cold day and the restaurant has a red hot heating element positioned about 10 feet above you that keeps you surprisingly warm. Heat from that element reaches you
(A) primarily via convection and conduction, with almost no heat flowing to you via radiation. [0.9% picked]
(B) primarily via convection and radiation, with almost no heat flowing to you via conduction. [4.4% picked]
(C) primarily via radiation, with almost no heat flowing to you via conduction or convection. [94.3% picked]
(D) equally well via conduction, convection, and radiation. [0.4% picked]
Answer: (C) primarily via radiation, with almost no heat flowing to you via conduction or convection. [94.3% picked]
Why: TBA
Problem 40:
The airflow around a dust particle is laminar. What force prevents that dust particle from falling rapidly to the ground and keeps it aloft for a long time?
(A) Viscous drag. [61.8% picked]
(B) Pressure drag. [5.3% picked]
(C) Lift. [31.1% picked]
(D) Induced drag. [1.8% picked]
Answer: (A) Viscous drag. [61.8% picked]
Why: TBA
Problem 41:
On a hot, humid day, the liquid perspiration on your wet skin doesn't do a very good job of cooling you off. The weather changes and the air suddenly becomes less humid, although its temperature remains the same. You find that you're cooling off better because water molecules now
(A) leave your wet skin more often, but land on your wet skin at the same rate as before. [18.9% picked]
(B) land on your wet skin less often, but leave your wet skin at the same rate as before. [69.7% picked]
(C) leave your wet skin less often, but land on your wet skin at the same rate as before. [3.5% picked]
(D) land on your wet skin more often, but leave your wet skin at the same rate as before. [7.9% picked]
Answer: (B) land on your wet skin less often, but leave your wet skin at the same rate as before. [69.7% picked]
Why: TBA
Problem 42:
You forgot to tip the bartender who brought a Shirley Temple drink to your luxury hotel suite. So you're leaning out over the balcony of your 20th floor suite and dropping solid gold marbles into the tip jar on the ground floor patio bar. You notice that it takes 4 seconds for each marble to fall into the jar, 20 floors below. When each marble has fallen for only 2 seconds, which floor of the hotel is it nearest? [Note: neglect any effects due to the air.]
(A) The marble is near the 8th floor. [3.5% picked]
(B) The marble is near the 12th floor. [2.2% picked]
(C) The marble is near the 10th floor. [0.4% picked]
(D) The marble is near the 15th floor. [93.9% picked]
Answer: (D) The marble is near the 15th floor. [93.9% picked]
Why: TBA
Problem 43:
If you're designing an energy efficient automobile, why should you minimize the diameter of the turbulent wake it leaves behind in the air?
(A) Since the automobile exhaust heats air in the wake, having less air in the wake means less heat extracted from the car. [14.9% picked]
(B) Since air in the wake has higher than atmospheric pressure, having less air in the wake means less pressure pushing on the rear of the car. [13.6% picked]
(C) Since air in the wake has higher than atmospheric density, having less air in the wake means less inertia to overcome. [3.9% picked]
(D) Since air in the wake has extracted forward momentum from the car, having less air in the wake means less extracted momentum. [67.5% picked]
Answer: (D) Since air in the wake has extracted forward momentum from the car, having less air in the wake means less extracted momentum. [67.5% picked]
Why: TBA
Problem 44:
You are riding a rollercoaster with a loop-the-loop. You have just rolled up the side of the loop and are, at this moment, exactly at the top of the loop. You and the car are upside down, yet you are pressed tightly into your seat. At this moment, you are accelerating
(A) upward at a rate equal in amount to the acceleration due to gravity. [7.0% picked]
(B) downward at the acceleration due to gravity. [8.8% picked]
(C) downward at more than the acceleration due to gravity. [80.7% picked]
(D) downward at less than the acceleration due to gravity. [3.5% picked]
Answer: (C) downward at more than the acceleration due to gravity. [80.7% picked]
Why: TBA
Problem 45:
Increasing the amount of carbon dioxide (a greenhouse gas) in the earth's atmosphere
(A) increases the rate at which the earth radiates heat into space. [16.7% picked]
(B) increases the altitude of the earth's effective radiating surface. [23.2% picked]
(C) has no effect on the earth's thermal radiation or the effective surface that emits that thermal radiation. [0.9% picked]
(D) decreases the rate at which the earth radiates heat into space. [58.8% picked]
Answer: (B) increases the altitude of the earth's effective radiating surface. [23.2% picked]
Why: TBA
Problem 46:
You place balls of cookie dough on a shiny metal cookie sheet and pop the sheet into the oven. The oven is being heated by an electric heating element at the bottom of the oven. How does heat flow from the heating element to the cookies?
(A) Primarily by convection of the air. [63.2% picked]
(B) Equally by conduction, convection, and radiation in the air. [17.5% picked]
(C) Primarily by conduction through the air. [5.7% picked]
(D) Primarily by radiation through the air. [13.6% picked]
Answer: (A) Primarily by convection of the air. [63.2% picked]
Why: TBA
Problem 47:
As water flows downward in a vertical pipe that has a uniform diameter, the water's gravitational potential energy decreases,
(A) its pressure potential energy increases, but its kinetic energy remains constant. [74.1% picked]
(B) both its pressure potential energy and its kinetic energy increase. [13.2% picked]
(C) its kinetic energy increases, but its pressure potential energy remains constant. [10.5% picked]
(D) neither its pressure potential energy nor its kinetic energy change. [2.2% picked]
Answer: (A) its pressure potential energy increases, but its kinetic energy remains constant. [74.1% picked]
Why: TBA
Problem 48:
Ice cannot be colder than
(A) 0 °F (-17.8°C). [7.0% picked]
(B) absolute zero. [73.2% picked]
(C) 32 °F (0 °C). [14.0% picked]
(D) -32 °F (-35.6 °C). [5.3% picked]
Answer: (B) absolute zero. [73.2% picked]
Why: TBA
Problem 49:
When smokejumpers parachute into forest fires, they have with them emergency tents made of shiny aluminum foil. If they're caught in the blaze, they lie flat on the dirt in a low spot with the aluminum tent propped just above them. If the fire passes quickly enough, they have a good chance of surviving it. The tent is made of aluminum because
(A) aluminum reflects most thermal radiation from the fire. [73.2% picked]
(B) aluminum does not conduct heat well. [19.7% picked]
(C) aluminum does not burn. [0.4% picked]
(D) aluminum blocks convective heat transfer from the fire. [6.6% picked]
Answer: (A) aluminum reflects most thermal radiation from the fire. [73.2% picked]
Why: TBA
Problem 50:
You are waterskiing at constant velocity on a calm lake while wearing a lifejacket. As you move across the water, you are doing
(A) zero work on the jacket and it is doing zero work on you. [93.9% picked]
(B) (positive) work on the jacket and it is doing negative work on you. [3.9% picked]
(C) negative work on the jacket and it is doing (positive) work on you. [0.4% picked]
(D) (positive) work on the jacket and it is doing (positive) work on you. [1.8% picked]
Answer: (A) zero work on the jacket and it is doing zero work on you. [93.9% picked]
Why: TBA
Problem 51:
Two guitar strings have the same tension and the same length, but one string is more massive than the other. When you pluck them both simultaneously, how do the fundamental pitches (frequencies) of the two strings compare?
(A) The more massive string has a higher pitch (larger frequency) than the less massive string. [2.2% picked]
(B) The two strings have the same pitch (same frequency) because they exhibit sympathetic vibration. [1.3% picked]
(C) The more massive string has a lower pitch (smaller frequency) than the less massive string. [91.7% picked]
(D) The two strings have the same pitch (same frequency) because the pitch (frequency) of a harmonic oscillators is independent of mass. [4.8% picked]
Answer: (C) The more massive string has a lower pitch (smaller frequency) than the less massive string. [91.7% picked]
Why: TBA
Problem 52:
An airplane is cruising horizontally at 30,000 feet and is traveling at constant velocity. The overall force that airplane exerts on the air points
(A) straight backward (toward the rear of the plane). [1.8% picked]
(B) downward and backward (toward the rear of the plane). [4.8% picked]
(C) downward and forward (toward the front of the plane). [3.9% picked]
(D) straight downward. [89.5% picked]
Answer: (D) straight downward. [89.5% picked]
Why: TBA
Problem 53:
Your winter jacket contains 8 ounces of goose down insulation, just enough to completely fill the interior of the jacket. Suppose you open the seams and tightly pack 8 more ounces of goose down insulation into the jacket. After sewing up the seams, your jacket will be
(A) twice as insulating as before, because goose down's thermal conductivity is proportional to one divided by its density. [28.9% picked]
(B) exactly as insulating as before because its thermal conductivity is determined only by its thickness, not by its contents. [21.9% picked]
(C) four times as insulating as before, because goose down's thermal conductivity is proportional to one divided by the square of its density. [19.3% picked]
(D) less insulating than before, because the excess goose down conducts heat better than the trapped air it replaces. [29.4% picked]
Answer: (D) less insulating than before, because the excess goose down conducts heat better than the trapped air it replaces. [29.4% picked]
Why: TBA
Problem 54:
You are waterskiing at constant velocity behind a powerful speedboat and your arms and legs are getting tired. The net force acting on you
(A) points directly forward. [8.8% picked]
(B) points directly upward. [7.0% picked]
(C) is zero. [79.8% picked]
(D) points forward and upward. [4.4% picked]
Answer: (C) is zero. [79.8% picked]
Why: TBA
Problem 55:
The second kind of perpetual motion machine provides an inexhaustible supply of mechanical work (or the equivalent of work), but consumes only heat from its constant-temperature environment. An example would be a black box that absorbs heat from the 70 °F room air and converts that heat into electricity forever. This form of perpetual motion machine is impossible because it
(A) violates the law of conservation of momentum. [0.4% picked]
(B) violates the law of thermal equilibrium. [11.8% picked]
(C) violates the law of entropy. [78.1% picked]
(D) violates the law of conservation of energy. [9.6% picked]
Answer: (C) violates the law of entropy. [78.1% picked]
Why: TBA
Problem 56:
If you're trying to increase the pressure in the water distribution system by modifying the local water tower, you should make the water tower
(A) taller. [96.1% picked]
(B) wider. [1.3% picked]
(C) narrower. [0.9% picked]
(D) shorter. [1.8% picked]
Answer: (A) taller. [96.1% picked]
Why: TBA
Problem 57:
Near sea level, water normally boils at about 212 °F (100 °C). However, a microwave oven can heat water in a glass container above that temperature if
(A) the glass container remains colder than 212 °F (100 °C). [7.9% picked]
(B) the glass container does not conduct electricity. [4.8% picked]
(C) the water is very pure. [5.7% picked]
(D) nothing helps form the initial steam bubbles. [81.6% picked]
Answer: (D) nothing helps form the initial steam bubbles. [81.6% picked]
Why: TBA
Problem 58:
A huge abstract iron sculpture has been installed in front of the local art museum. It sits there motionless, "guarding" the main doorway. The sculpture is experiencing two forces: its weight downward and a force upward from the brick courtyard beneath it. We know that these two forces on the sculpture are equal in amount but oppositely directed because
(A) the sculpture has zero velocity. [1.8% picked]
(B) Newton's third law requires that forces always appear in equal but oppositely directed pairs. [3.9% picked]
(C) for every action, there is an equal but oppositely directed reaction. [1.3% picked]
(D) the sculpture is not accelerating, so the two forces must sum to zero. [93.0% picked]
Answer: (D) the sculpture is not accelerating, so the two forces must sum to zero. [93.0% picked]
Why: TBA
Problem 59:
To win a stuffed animal at the state fair, you simply need to drop a glass marble onto a stationary glass plate and have the marble come to rest on that plate. Unfortunately, when the marble hits the plate, it bounces upward because the marble
(A) retains essentially all of its energy but transfers a large amount of momentum to the plate. [92.5% picked]
(B) retains essentially all of its energy and momentum. [3.1% picked]
(C) transfers a large amount of momentum and energy to the plate. [0.4% picked]
(D) retains essentially all of its momentum but transfers a large amount of energy to the plate. [3.9% picked]
Answer: (A) retains essentially all of its energy but transfers a large amount of momentum to the plate. [92.5% picked]
Why: TBA
Problem 60:
Once a baseball leaves the pitcher's hand and is heading toward home plate, it gradually slows down. The primary reason for this slowing is that the air pressure
(A) at the front and back of the ball is less than atmospheric pressure, while the pressure on the sides of the ball is more than atmospheric. [2.2% picked]
(B) at the front and back of the ball is greater than atmospheric pressure, while the pressure on the sides of the ball is less than atmospheric. [9.2% picked]
(C) at the front of the ball is equal to atmospheric pressure, while the pressure behind the ball is less than atmospheric. [3.5% picked]
(D) at the front of the ball is greater than atmospheric pressure, while the pressure behind the ball is approximately atmospheric. [85.1% picked]
Answer: (D) at the front of the ball is greater than atmospheric pressure, while the pressure behind the ball is approximately atmospheric. [85.1% picked]
Why: TBA