Final Examination Solutions

Physics 1050 - Fall 2016 - Final Exam - Posted Version with Solutions

Problem 1:
While decorating your new guitar, you accidently coat one of the guitar strings with spray paint. That paint increases the string's mass. How will that change affect the string?
(A) The string's frequency of vibration (pitch) will not change, but its amplitude of motion will decrease. [4.7% picked]
(B) The string's frequency of vibration (pitch) will not change, but its amplitude of motion will increase. [1.7% picked]
(C) The string's frequency of vibration (pitch) will decrease. [88.9% picked]
(D) The string's frequency of vibration (pitch) will increase. [4.7% picked]
Answer: (C) The string's frequency of vibration (pitch) will decrease. [88.9% picked]
Why: TBA
Problem 2:
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) your cousin. [1.3% picked]
(B) neither of you. It was instead provided by chemical potential energy in the wishbone itself. [0.9% picked]
(C) you. [93.6% picked]
(D) both you and your cousin. [4.3% picked]
Answer: (C) you. [93.6% picked]
Why: TBA
Problem 3:
After clearing the bar in the high jump, you land softly on a giant mattress. Landing on the mattress is much more comfortable than landing on a sand heap of equal size because
(A) you transfer the same momentum to the mattress in coming to a stop as you would have transferred to the sand heap in coming to a stop, but the mattress takes more time to stop you. [97.9% picked]
(B) you transfer the same momentum to the mattress in coming to a stop as you would have transferred to the sand heap in coming to a stop, but the mattress has more mass than the sand. [0.4% picked]
(C) you transfer less momentum to the mattress in coming to a stop than you would have transferred to the sand heap in coming to a stop. [0.0% picked]
(D) you transfer more momentum to the mattress in coming to a stop than you would have transferred to the sand heap in coming to a stop. [1.7% picked]
Answer: (A) you transfer the same momentum to the mattress in coming to a stop as you would have transferred to the sand heap in coming to a stop, but the mattress takes more time to stop you. [97.9% picked]
Why: TBA
Problem 4:
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) smaller on higher floors. [3.8% picked]
(B) the same on all floors, but the speed of the spraying water is greater on higher floors. [4.3% picked]
(C) greater on higher floors. [2.1% picked]
(D) the same on all floors, but the speed of the spraying water is smaller on higher floors. [89.8% picked]
Answer: (D) the same on all floors, but the speed of the spraying water is smaller on higher floors. [89.8% picked]
Why: TBA
Problem 5:
What change can you make to a pendulum to increase its period of oscillation—that is, the time it takes to complete one full cycle of oscillation?
(A) Increase the length of the pendulum. [87.7% picked]
(B) Increase the amplitude of the pendulum's motion (the spatial extent of its motion). [4.7% picked]
(C) Increase the acceleration due to gravity. [4.3% picked]
(D) Increase the mass of the pendulum. [3.4% picked]
Answer: (A) Increase the length of the pendulum. [87.7% picked]
Why: TBA
Problem 6:
Two cans of soup, one of which weighs twice as much as the other, roll off of a horizontal table together at the same initial velocity. In this situation,
(A) both cans hit the floor at approximately the same time, but the heavier can lands considerably farther from the table than the lighter can does. [6.4% picked]
(B) the heavier can hits the floor first and it lands considerably farther from the table than the lighter can does. [0.0% picked]
(C) both cans hit the floor at approximately the same time and at the same distance from the table. [93.2% picked]
(D) the heavier can hits the floor first and it lands considerably closer to the table than the lighter can does. [0.4% picked]
Answer: (C) both cans hit the floor at approximately the same time and at the same distance from the table. [93.2% picked]
Why: TBA
Problem 7:
Firefighters are battling a fire on the 10th floor of an apartment building. When they stand on the ground, water flowing through their firehose from their firetruck can only shoot the water up to the 8th floor. So they carry the end of the same fire hose up a 2-story-tall ladder and again start shooting water upward. Now the water rises to the
(A) 6th floor. [0.4% picked]
(B) 10th floor. [7.7% picked]
(C) 9th floor. [0.4% picked]
(D) 8th floor. [91.5% picked]
Answer: (D) 8th floor. [91.5% picked]
Why: TBA
Problem 8:
Winds are powered by temperature differences at the Earth's surface. As those temperature differences grow larger with climate change, the winds may also grow stronger. Why are larger temperature difference capable of producing stronger winds?
(A) The greater the temperature difference, the less entropy is produced by each joule of heat that flows from hot to cold and the larger the fraction of heat that can be diverted as work. [15.7% picked]
(B) The greater the temperature difference, the less entropy is produced by each joule of heat that flows from hot to cold and the more work remains available to power the winds. [4.7% picked]
(C) The greater the temperature difference, the more entropy is produced by each joule of heat that flows from hot to cold and the larger the fraction of heat that can be diverted as work. [49.4% picked]
(D) The greater the temperature difference, the more entropy is produced by each joule of heat that flows from hot to cold and the more of that entropy that can be converted into work. [30.2% picked]
Answer: (C) The greater the temperature difference, the more entropy is produced by each joule of heat that flows from hot to cold and the larger the fraction of heat that can be diverted as work. [49.4% picked]
Why: TBA
Problem 9:
When the A-string of a guitar vibrates in its fundamental mode without anyone touching it, it has a frequency (or pitch) of 110 cycles per second. When that same string is vibrating at 330 cycles per second without anyone touching it, it is vibrating in its
(A) fundamental mode just as before, but completing the same motion 3 times as quickly. [11.1% picked]
(B) fundamental mode, but traveling 3 times as far during each vibrational cycle. [2.6% picked]
(C) third harmonic mode, as three 1/3rd-length strings. [80.9% picked]
(D) fundamental mode, but traveling 1/3rd as far during each vibrational cycle. [5.5% picked]
Answer: (C) third harmonic mode, as three 1/3rd-length strings. [80.9% picked]
Why: TBA
Problem 10:
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 less than the local atmospheric pressure. [86.4% picked]
(B) 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. [6.4% picked]
(C) The airstream over the wing is traveling straight ahead, so the pressure just above the wing must equal the local atmospheric pressure. [0.0% 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. [7.2% picked]
Answer: (A) 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. [86.4% picked]
Why: TBA
Problem 11:
The maximum speed of a rocket-propelled spaceship with an exhaust speed of 5000 mph is
(A) limited only by the ratio of fuel to spaceship. [55.7% picked]
(B) 2500 mph. [3.4% picked]
(C) 10000 mph. [2.1% picked]
(D) 5000 mph. [38.7% picked]
Answer: (A) limited only by the ratio of fuel to spaceship. [55.7% picked]
Why: TBA
Problem 12:
During the power stroke in one cylinder of a car's engine, the burned fuel and air push the piston out of the cylinder. In accordance with Newton's third law, the piston pushes back on the burned gas. Overall, the
(A) burned gas does work on the piston and the gas experiences a rise in temperature. [18.3% picked]
(B) piston does work on the burned gas and the gas experiences a rise in temperature. [8.5% picked]
(C) burned gas does work on the piston and the gas experiences a drop in temperature. [68.5% picked]
(D) piston does work on the burned gas and the gas experiences a drop in temperature. [4.7% picked]
Answer: (C) burned gas does work on the piston and the gas experiences a drop in temperature. [68.5% picked]
Why: TBA
Problem 13:
On a humid summer day, perspiration doesn't cool you off much because
(A) the air's relative humidity is almost 100%, so there is almost no evaporation. [67.2% picked]
(B) the air density is extremely low and its pressure is too low to permit water to evaporate. [6.0% picked]
(C) the water vapor in the air is moving too fast to condense on your skin as perspiration. [13.2% picked]
(D) the air density is extremely low and its pressure is too high to permit water to evaporate. [13.6% picked]
Answer: (A) the air's relative humidity is almost 100%, so there is almost no evaporation. [67.2% picked]
Why: TBA
Problem 14:
You drop a cylindrical can of soup and its flat bottom lands hard on the cement floor. As the result of the liquid-filled can's violent impact with the floor, its sides bulge outward. The bulge(s) is/are located at the
(A) bottom of the can. [88.9% picked]
(B) top and bottom of the can, leaving the middle of the can unaffected. [0.4% picked]
(C) middle of the can. [6.0% picked]
(D) top of the can. [4.7% picked]
Answer: (A) bottom of the can. [88.9% picked]
Why: TBA
Problem 15:
While most western musical instruments are based on harmonic oscillators, there are some instruments that are not harmonic oscillators. What feature of an instrument's sound would indicate that it is not a harmonic oscillator?
(A) A rapid decrease in the loudness of its sound. [6.8% picked]
(B) A change in its pitch (vibrational frequency) as the loudness of its sound decreases. [63.0% picked]
(C) A rapid increase in the loudness of its sound. [1.7% picked]
(D) The absence of a change in its pitch (vibrational frequency) as the loudness of its sound decreases. [28.5% picked]
Answer: (B) A change in its pitch (vibrational frequency) as the loudness of its sound decreases. [63.0% picked]
Why: TBA
Problem 16:
Why must a sprinter lean forward as she picks up speed at the start of a race?
(A) She must lean in the direction of her velocity in order to increase that forward velocity. [6.8% picked]
(B) By leaning forward, she can use her weight to make her accelerate forward at the acceleration due to gravity. [7.7% picked]
(C) Her forward lean moves her closer to the finish line so that she arrives sooner. [0.0% picked]
(D) If she stood upright as the ground pushed her feet forward, the inertia of her upper body would cause her to tip over backward. [85.5% picked]
Answer: (D) If she stood upright as the ground pushed her feet forward, the inertia of her upper body would cause her to tip over backward. [85.5% picked]
Why: TBA
Problem 17:
Your French fries are getting cold as you wait for your server to bring you a new bottle of ketchup. In frustration, you decide to get the last bits of ketchup out of the old bottle by swinging it rapidly in a circle with the cap-end of the bottle pointing away from you. This technique works because
(A) the bottle's rapid inward acceleration leaves the ketchup behind so that it drifts toward the cap-end of the bottle. [91.1% picked]
(B) centrifugal force pushes the ketchup toward the cap-end of the bottle. [4.7% picked]
(C) viscous forces push the ketchup toward the cap-end of the bottle. [1.7% picked]
(D) the force of the ketchup's momentum pushes it toward the cap-end of the bottle. [2.6% picked]
Answer: (A) the bottle's rapid inward acceleration leaves the ketchup behind so that it drifts toward the cap-end of the bottle. [91.1% picked]
Why: TBA
Problem 18:
It is a beautiful summer day and the residents of a high-rise apartment building are eating dinner on their balconies. A resident accidentally knocks an empty glass off a balcony that is about 80 meters (260 feet) above the cement patio. The glass would have smashed on that patio after falling for 4 seconds, however, a quick-witted resident catches the glass after it has fallen for only 2 seconds. How far above the patio was the glass when it was caught?
(A) Approximately 50 meters above the patio. [9.4% picked]
(B) Approximately 30 meters above the patio. [4.7% picked]
(C) Approximately 60 meters above the patio. [84.3% picked]
(D) Approximately 40 meters above the patio. [1.7% picked]
Answer: (C) Approximately 60 meters above the patio. [84.3% picked]
Why: TBA
Problem 19:
You drop an extremely bouncy rubber ball on a cement floor and it rebounds upward almost to its original height. Compare the ball's energy and momentum just before it bounced on the floor with its energy and momentum just after bounced off the floor.
(A) The ball's energy and momentum changed significantly. [0.0% picked]
(B) The ball's energy changed only a little, but its momentum changed significantly. [90.6% picked]
(C) The ball's energy and momentum changed only a little. [5.5% picked]
(D) The ball's energy changed significantly, but its momentum changed only a little. [3.8% picked]
Answer: (B) The ball's energy changed only a little, but its momentum changed significantly. [90.6% picked]
Why: TBA
Problem 20:
When the cylinder in an automobile's engine is going through the compression stroke, the piston squeezes the fuel and air mixture into a smaller volume within the cylinder. As the piston moves into the cylinder, the piston does work on the fuel and air mixture and
(A) the pressure, density, and temperature of the gas all increase. [74.5% picked]
(B) the pressure and temperature of the gas increase, but the density of the gas remains unchanged. [16.6% picked]
(C) the pressure and density of gas increase, but the temperature of the gas remains unchanged. [5.1% picked]
(D) the density and temperature of the gas increase, but the pressure of the gas remains unchanged. [3.8% picked]
Answer: (A) the pressure, density, and temperature of the gas all increase. [74.5% picked]
Why: TBA
Problem 21:
When water rushing through a hose flows around a bend in that hose, its pressure changes. The water pressure
(A) increases near the inside of the bend and increases near the outside of the bend. [0.4% picked]
(B) increases near the inside of the bend and decreases near the outside of the bend. [7.2% picked]
(C) decreases near the inside of the bend and decreases near the outside of the bend. [0.4% picked]
(D) decreases near the inside of the bend and increases near the outside of the bend. [91.9% picked]
Answer: (D) decreases near the inside of the bend and increases near the outside of the bend. [91.9% picked]
Why: TBA
Problem 22:
When you light a candle, its flame turns wax molecules and oxygen into water and carbon dioxide molecules. The molecules that form during this combustion have
(A) less chemical potential energy than the original wax and oxygen molecules. [93.2% picked]
(B) more chemical potential energy than the original wax and oxygen molecules. [4.3% picked]
(C) less chemical momentum than the original wax and oxygen molecules. [1.7% picked]
(D) more chemical momentum than the original wax and oxygen molecules. [0.9% picked]
Answer: (A) less chemical potential energy than the original wax and oxygen molecules. [93.2% picked]
Why: TBA
Problem 23:
Since a water molecule weighs less than the average air molecule, humid air is less dense than dry air. Suppose that the humidity of the air increases significantly during an orchestra concert. How will the resulting decrease in air density affect the wind instruments (e.g., flutes, clarinets, oboes)?
(A) Their pitches (frequencies of vibration) will decrease. [7.3% picked]
(B) Their loudnesses (amplitudes of vibration) will increase. [3.4% picked]
(C) Their pitches (frequencies of vibration) will increase. [85.0% picked]
(D) Their loudnesses (amplitudes of vibration) will decrease. [4.3% picked]
Answer: (C) Their pitches (frequencies of vibration) will increase. [85.0% picked]
Why: TBA
Problem 24:
One warm spring day you and some friends go to the beach at a nearby lake. The beach ball you are playing with is not quite fully inflated, so the pressure inside it is atmospheric. Someone accidentally knocks the ball into the lake. Although it is a very hot day, the water is very cold and nobody wants to retrieve the ball. You notice that the ball seems to have deflated somewhat after sitting in the water for a while. The contact with the cool water has caused the temperature of the air inside the ball to drop, resulting in a significant
(A) decrease in the density of the air inside the ball. [9.4% picked]
(B) decrease in the pressure inside the ball. [24.7% picked]
(C) increase in the density of the air inside the ball. [64.7% picked]
(D) increase in the pressure inside the ball. [1.3% picked]
Answer: (C) increase in the density of the air inside the ball. [64.7% picked]
Why: TBA
Problem 25:
An automobile engine "knocks" when the gas in its cylinder ignites spontaneously rather than waiting for the sparkplug to ignite it. During which of the 4 strokes can this premature ignition occur?
(A) The compression stroke (when the gas in the cylinder is being compressed). [92.3% picked]
(B) The intake stroke (when gas is being added to the cylinder). [2.6% picked]
(C) The exhaust stroke (when gas is being ejected from the cylinder). [1.3% picked]
(D) The power stroke (when the gas in the cylinder is pushing the piston out of the cylinder). [3.8% picked]
Answer: (A) The compression stroke (when the gas in the cylinder is being compressed). [92.3% picked]
Why: TBA
Problem 26:
When you pull a pendulum away from equilibrium and let go, the pendulum swings back and forth rhythmically for a very long time. What physical quantity keeps it going for so long?
(A) Momentum that the pendulum cannot get rid of easily. [51.5% picked]
(B) Mass that the pendulum cannot get rid of easily. [3.0% picked]
(C) Energy that the pendulum cannot get rid of easily. [43.4% picked]
(D) Entropy that the pendulum cannot get rid of easily. [2.1% picked]
Answer: (C) Energy that the pendulum cannot get rid of easily. [43.4% picked]
Why: TBA
Problem 27:
If a golf ball were smooth rather than dimpled, it would
(A) curve toward the right after being hit by the club of a right-handed golfer. [0.4% picked]
(B) not travel as far after being hit by a golf club. [96.2% picked]
(C) travel much farther after being hit by a golf club. [2.1% picked]
(D) curve toward the left after being hit by the club of a right-handed golfer. [1.3% picked]
Answer: (B) not travel as far after being hit by a golf club. [96.2% picked]
Why: TBA
Problem 28:
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 helium-filled balloon's weight decreases as you put more lightweight helium particles inside it and eventually it becomes weightless. [6.0% picked]
(B) 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. [6.4% picked]
(C) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases much faster and eventually the buoyant force exceeds the balloon's weight. [83.0% picked]
(D) the upward buoyant force on a balloon full of helium is larger than the buoyant force on an identical balloon full of air. [4.7% picked]
Answer: (C) the weight of the helium-filled balloon increases as it fills, but the buoyant force it experiences increases much faster and eventually the buoyant force exceeds the balloon's weight. [83.0% picked]
Why: TBA
Problem 29:
A typical heat pump (an air conditioner run backwards so that it heats the indoor air) consumes 2000 watts of electric power. How much thermal power does it provide to the indoor air?
(A) Significantly more than 2000 watts. [84.7% picked]
(B) About 1800 watts. [1.7% picked]
(C) About 2000 watts. [10.6% picked]
(D) About 200 watts. [3.0% picked]
Answer: (A) Significantly more than 2000 watts. [84.7% picked]
Why: TBA
Problem 30:
You are drying your hair and you have put a diffuser (an anti-nozzle) on the end of the dryer. As it goes through the diffuser, the air slows down and its
(A) pressure increases. [82.1% picked]
(B) momentum increases. [0.4% picked]
(C) density decreases. [11.9% picked]
(D) particle density decreases. [5.5% picked]
Answer: (A) pressure increases. [82.1% picked]
Why: TBA
Problem 31:
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 without changing its dimensions at all. 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. [4.7% picked]
(B) four times as insulating as before, because goose down's thermal conductivity is proportional to one divided by the square of its density. [0.9% picked]
(C) less insulating than before, because the excess goose down conducts heat better than the trapped air it replaces. [91.5% picked]
(D) exactly as insulating as before because its thermal conductivity is determined only by its thickness, not by its contents. [3.0% picked]
Answer: (C) less insulating than before, because the excess goose down conducts heat better than the trapped air it replaces. [91.5% picked]
Why: TBA
Problem 32:
An air conditioner's compressor takes low density gas and compresses that gas to high density and that gas begins to condense into a liquid. Why does compressing the gas cause it to condense?
(A) Compression removes entropy from the gas so that has to become a liquid. [6.0% picked]
(B) Compression causes the temperature of the gas to decrease so that it condenses into a liquid. [13.6% picked]
(C) Increasing the density of the gas removes its latent heat of evaporation and forces it to become a liquid. [28.1% picked]
(D) The rate at which molecules land on the liquid from the gas exceeds the rate at which molecules leave the liquid for the gas. [52.3% picked]
Answer: (D) The rate at which molecules land on the liquid from the gas exceeds the rate at which molecules leave the liquid for the gas. [52.3% picked]
Why: TBA
Problem 33:
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 are forcing convection to occur so that heat flows more rapidly from the cup to the coffee. [1.7% picked]
(B) You are encouraging the conduction of heat from the cup to the coffee. [2.1% picked]
(C) You do work on the coffee as you stir it and viscous effects turn that work into thermal energy. [94.9% picked]
(D) You are making the coffee move as though it were boiling, so that it becomes hotter. [1.3% picked]
Answer: (C) You do work on the coffee as you stir it and viscous effects turn that work into thermal energy. [94.9% picked]
Why: TBA
Problem 34:
In its fundamental vibrational mode, a guitar string vibrates as a single string. In its second harmonic mode, the string vibrates as two half-strings. How do those two vibrations differ?
(A) The amplitude and loudness of the second harmonic mode is half that of the fundamental mode. [1.7% picked]
(B) The frequency (number of vibrational cycles per second) of the second harmonic mode is half that of the fundamental mode. [7.7% picked]
(C) The amplitude and loudness of the second harmonic mode is twice that of the fundamental mode. [1.7% picked]
(D) The frequency (number of vibrational cycles per second) of the second harmonic mode is twice that of the fundamental mode. [88.9% picked]
Answer: (D) The frequency (number of vibrational cycles per second) of the second harmonic mode is twice that of the fundamental mode. [88.9% picked]
Why: TBA
Problem 35:
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. [89.8% picked]
(B) Upward and eastward. [6.0% picked]
(C) Upward and westward. [1.3% picked]
(D) Downward and eastward. [3.0% picked]
Answer: (A) Downward and westward. [89.8% picked]
Why: TBA
Problem 36:
A metal ball hanging from a coil spring can bounce up and down as a harmonic oscillator. Which of the following changes will increase the ball's period—that is, the time it takes the ball to complete one full cycle of its bouncing motion?
(A) Decrease the amplitude of the ball's motion—that is, the extent of the ball's motion above and below equilibrium. [2.6% picked]
(B) Increase the ball's mass. [50.6% picked]
(C) Increase the amplitude of the ball's motion—that is, the extent of the ball's motion above and below equilibrium. [21.3% picked]
(D) Increase the spring's stiffness. [25.5% picked]
Answer: (B) Increase the ball's mass. [50.6% picked]
Why: TBA
Problem 37:
If you try to cook vegetables with 100 °C air, it takes a long time. But if you cook those same vegetables with 100 °C steam, they cook quickly. This is because the steam
(A) condenses on the colder vegetables and releases a large amount of heat to the vegetables. [94.0% picked]
(B) causes moisture inside the vegetables to boil and absorb heat from the vegetables. [1.7% picked]
(C) condenses on the colder vegetables and absorbs a large amount of heat from the vegetables. [0.9% picked]
(D) causes moisture inside the vegetables to boil and transfer heat to the vegetables. [3.4% picked]
Answer: (A) condenses on the colder vegetables and releases a large amount of heat to the vegetables. [94.0% picked]
Why: TBA
Problem 38:
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) doing work on the bucket and the bucket is doing work on the cement it contains. [93.2% picked]
(B) not doing work on the bucket, but the bucket is doing work on the cement it contains. [0.9% picked]
(C) doing work on the bucket, but the bucket is not doing work on the cement it contains. [3.0% picked]
(D) not doing work on the bucket or the cement it contains. [3.0% picked]
Answer: (A) doing work on the bucket and the bucket is doing work on the cement it contains. [93.2% picked]
Why: TBA
Problem 39:
Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand removes less energy from you because it
(A) stops the downward motion of your foot faster and thus absorbs less of your momentum. [11.5% picked]
(B) barely moves downward as you push downward on it, so you do almost zero work on it. [79.1% picked]
(C) stops the downward motion of your foot faster and thus absorbs more of your momentum. [1.7% picked]
(D) pushes up on your foot just as hard as your foot pushes down on it, unlike the soft dry sand. [7.7% picked]
Answer: (B) barely moves downward as you push downward on it, so you do almost zero work on it. [79.1% picked]
Why: TBA
Problem 40:
You remove a plastic container and its lid from the hot dishwasher. After snapping the lid on the container, you put the sealed container of air on the counter to cool. When you examine the container later, you find that its lid has bowed inward significantly, reducing the container's volume. How has the cooling process affected the air pressure and air density in the container?
(A) The air's pressure has increased and its density has decreased. [8.5% picked]
(B) The air's pressure has increased and its density has increased. [7.3% picked]
(C) The air's pressure has decreased and its density has increased. [80.8% picked]
(D) The air's pressure has decreased and its density has decreased. [3.4% picked]
Answer: (C) The air's pressure has decreased and its density has increased. [80.8% picked]
Why: TBA
Problem 41:
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 lighter than the boy. [4.3% picked]
(B) the girl is riding on a much taller swing than the boy is riding. [0.0% picked]
(C) the girl is much heavier than the boy. [1.3% picked]
(D) the girl is riding on a much shorter swing than the boy is riding. [94.5% picked]
Answer: (D) the girl is riding on a much shorter swing than the boy is riding. [94.5% picked]
Why: TBA
Problem 42:
Your new dorm room is too hot in the summer, so you decide to install a window air conditioning unit. Since your room has no window, you install the air conditioner between your room and a suitemate's room. When you plug it in and turn it on, the unit transfers heat from your room to your suitemate's room and your room becomes pleasantly cool. As the unit does its job, what is happening to entropy?
(A) The entropy of your room is decreasing, the entropy of your suitemate's room is increasing, and the total entropy is not decreasing. [77.0% picked]
(B) The entropy of your room is increasing, the entropy of your suitemate's room is decreasing, and the total entropy is constant. [10.2% picked]
(C) The entropy of your room is increasing, the entropy of your suitemate's room is increasing. [8.5% picked]
(D) The entropy of your room is decreasing, the entropy of your suitemate's room is decreasing. [4.3% picked]
Answer: (A) The entropy of your room is decreasing, the entropy of your suitemate's room is increasing, and the total entropy is not decreasing. [77.0% picked]
Why: TBA
Problem 43:
Water is flowing through a horizontal pipe in laminar, steady-state flow. Halfway along the pipe, its diameter decreases and the water must continue on through that narrow second half. Compared to when it was in the wide first half of the pipe, water in the narrow second half of the pipe is moving
(A) slower and its pressure is smaller. [1.3% picked]
(B) faster and its pressure is larger. [21.9% picked]
(C) slower and its pressure is larger. [39.9% picked]
(D) faster and its pressure is smaller. [36.9% picked]
Answer: (D) faster and its pressure is smaller. [36.9% picked]
Why: TBA
Problem 44:
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. [2.1% picked]
(B) The glass of salt water has more entropy. [90.6% picked]
(C) They have the same entropy because water's entropy is independent of its purity. [2.6% picked]
(D) The glass of pure water with salt at its bottom has more entropy. [4.7% picked]
Answer: (B) The glass of salt water has more entropy. [90.6% picked]
Why: TBA
Problem 45:
A tall flagpole is topped by a metal ball. When a large bird leaps off the ball, the flagpole starts bending back and forth rhythmically about its straight equilibrium shape. At what moment(s) during its rhythmic motion is the ball moving fastest?
(A) Just before the flagpole is bent furthest away from equilibrium. [1.7% picked]
(B) When the ball is coasting through equilibrium. [90.6% picked]
(C) When the flagpole is bent furthest away from equilibrium. [2.6% picked]
(D) Just after the flagpole is bent furthest away from equilibrium. [5.1% picked]
Answer: (B) When the ball is coasting through equilibrium. [90.6% picked]
Why: TBA
Problem 46:
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 air in the wake has higher than atmospheric density, having less air in the wake means less inertia to overcome. [3.0% picked]
(B) Since air in the wake has extracted forward momentum from the car, having less air in the wake means less extracted momentum. [84.3% picked]
(C) Since the automobile exhaust heats air in the wake, having less air in the wake means less heat extracted from the car. [7.2% picked]
(D) 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. [5.5% picked]
Answer: (B) Since air in the wake has extracted forward momentum from the car, having less air in the wake means less extracted momentum. [84.3% picked]
Why: TBA
Problem 47:
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 temperature: 1800 °C. They remain solid. Which one is glowing most brightly?
(A) They are all glowing with equal brightness. [2.6% picked]
(B) The object that originally appeared shiny. [2.1% picked]
(C) The object that originally appeared white. [0.9% picked]
(D) The object that original appeared black. [94.5% picked]
Answer: (D) The object that original appeared black. [94.5% picked]
Why: TBA
Problem 48:
You are driving Northward on a highway when you come to a smooth 90° turn toward the right. You maintain a constant speed around the turn and are soon driving Eastward. During the middle of the turn, in which direction were you accelerating?
(A) You were accelerating toward the Southeast. [63.4% picked]
(B) You were accelerating toward the East. [12.3% picked]
(C) You were accelerating toward the South. [1.3% picked]
(D) You were accelerating toward the Northeast. [23.0% picked]
Answer: (A) You were accelerating toward the Southeast. [63.4% picked]
Why: TBA
Problem 49:
If you strike a stiff, spring-like surface with a mallet and listen to the sound it emits, you'll notice that this sound is more complicated than that emitted by a string or a thin bar. That's because surfaces
(A) are not harmonic oscillators. [12.8% picked]
(B) have overtones that are not integer multiples of their fundamental frequencies. [68.5% picked]
(C) are harmonic oscillators. [3.0% picked]
(D) have overtones that are integer multiples of their fundamental frequencies. [15.7% picked]
Answer: (B) have overtones that are not integer multiples of their fundamental frequencies. [68.5% picked]
Why: TBA
Problem 50:
Two photographs show the same thermally isolated room containing the same air molecules, water molecules, and ceramic mug. In one photograph, the air is moist and the mug is empty. In the other photograph, the air is dry and the mug contains liquid water. Of these two photographs, the situation in which the air is moist and the mug is empty has
(A) more entropy and less thermal energy. [23.9% picked]
(B) more entropy and more thermal energy. [70.1% picked]
(C) less entropy and less thermal energy. [2.6% picked]
(D) less entropy and move thermal energy. [3.4% picked]
Answer: (A) more entropy and less thermal energy. [23.9% picked]
Why: TBA
Problem 51:
When you pour milk from a pitcher into a bowl, the flow is likely to become turbulent. When you pour honey from a jar into a bowl, however, the flow is likely to remain laminar. Compared to milk, honey is more likely to exhibit laminar flow because honey's larger
(A) weight tends to keep the flow orderly. [0.0% picked]
(B) density tends to keep the flow orderly. [3.8% picked]
(C) viscosity tends to keep the flow orderly. [96.2% picked]
(D) inertia tends to keep the flow orderly. [0.0% picked]
Answer: (C) viscosity tends to keep the flow orderly. [96.2% picked]
Why: TBA
Problem 52:
The hotter it is outside, the more electric energy an air conditioner must use to remove each joule of heat from the 72 °F indoor air in your home. It must consume more electric energy on a hotter day because
(A) delivering that joule of heat to the outdoor air creates more entropy as the outdoor air gets hotter. [18.7% picked]
(B) removing that joule of heat from the 72 ° indoor air creates more entropy on a hotter day. [9.8% picked]
(C) delivering that joule of heat to the outdoor air creates less entropy as the outdoor air gets hotter. [66.4% picked]
(D) entropy flows into your home faster when the outdoor air is hotter. [5.1% picked]
Answer: (C) delivering that joule of heat to the outdoor air creates less entropy as the outdoor air gets hotter. [66.4% picked]
Why: TBA
Problem 53:
Your bottle of oil and vinegar salad dressing has separated, so that the oil is floating on the vinegar. You notice that a large herb is floating motionless at the interface between the oil and the vinegar. That herb's average density is
(A) less than that of vinegar but more than that of oil. [78.7% picked]
(B) more than that of either vinegar or oil. [0.0% picked]
(C) less than that of either vinegar or oil. [1.7% picked]
(D) less than that of oil but more than that of vinegar. [19.6% picked]
Answer: (A) less than that of vinegar but more than that of oil. [78.7% picked]
Why: TBA
Problem 54:
A seemingly "haunted" house emits creaking sounds as it cools off at night. Since sound carries energy, the house must obtain that energy from somewhere (other than ghosts and goblins). While this energy begins as thermal energy, the sound doesn't appear until the outside temperature drops well below the temperature of the house because
(A) building materials become too soft during the day to vibrate with enough efficiency to convert thermal energy into sound energy. [3.4% picked]
(B) sound, like heat, can only flow from hotter objects to colder objects. [0.4% picked]
(C) the house's thermal energy increases most rapidly after dark. [0.0% picked]
(D) the house's thermal energy can only become work and sound as heat flows from the hotter house to the colder outside air. [96.2% picked]
Answer: (D) the house's thermal energy can only become work and sound as heat flows from the hotter house to the colder outside air. [96.2% picked]
Why: TBA
Problem 55:
A satellite is orbiting the earth in a not-quite-circular orbit. As it moves, the satellite is accelerating
(A) directly outward, away from the center of the earth. [1.3% picked]
(B) nearly forward, in the direction of a perfect circle around the earth. [1.7% picked]
(C) directly toward the center of the earth. [97.0% picked]
(D) exactly forward, in the direction that the satellite is heading. [0.0% picked]
Answer: (C) directly toward the center of the earth. [97.0% picked]
Why: TBA
Problem 56:
Increasing the amount of carbon dioxide (a greenhouse gas) in the earth's atmosphere
(A) increases the altitude of the earth's effective radiating surface. [74.0% picked]
(B) has no effect on the earth's thermal radiation or the effective surface that emits that thermal radiation. [0.9% picked]
(C) decreases the rate at which the earth radiates heat into space. [18.3% picked]
(D) increases the rate at which the earth radiates heat into space. [6.8% picked]
Answer: (A) increases the altitude of the earth's effective radiating surface. [74.0% picked]
Why: TBA
Problem 57:
You are cleaning the siding on your house by spraying water at it from a hose and nozzle. At the center of the stream of water, right where it hits the siding, the water is coming to a complete stop. The pressure in the water at the center of the stream as it touches the siding is
(A) exactly zero. [2.6% picked]
(B) higher than atmospheric pressure. [91.5% picked]
(C) equal to atmospheric pressure. [3.4% picked]
(D) lower than atmospheric pressure, but more than zero. [2.6% picked]
Answer: (B) higher than atmospheric pressure. [91.5% picked]
Why: TBA
Problem 58:
A bottle in both thermal and phase equilibrium at 0 °C contains 1 kilogram of ice and 1 kilogram of liquid water. You move the bottle to a new location and allow it to reach equilibrium at 0.5 °C. The bottle now contains
(A) 1 kilogram of ice and 1 kilogram of liquid water. [3.0% picked]
(B) 2 kilograms of liquid water. [91.1% picked]
(C) 1.5 kilograms of ice and 0.5 kilograms of liquid water. [0.9% picked]
(D) 0.5 kilograms of ice and 1.5 kilograms of liquid water. [5.1% picked]
Answer: (B) 2 kilograms of liquid water. [91.1% picked]
Why: TBA
Problem 59:
If you pluck a guitar string at different points along its length, it will produce somewhat different sounds. What is different about the string when you pluck it at different points?
(A) The string can vibrate simultaneously in its fundamental and harmonic vibrational modes, and the mixture of those different vibrations depends on where you pluck it. [52.3% picked]
(B) The string's fundamental vibrational frequency depends on its amplitude of vibration and that amplitude depends on where you pluck the string. [26.0% picked]
(C) Where you pluck the string divides the string into two parts that vibrate separately, so where you pluck affects those two partial strings. [13.2% picked]
(D) The string's fundamental vibrational frequency depends on where you plucking it. [8.5% picked]
Answer: (A) The string can vibrate simultaneously in its fundamental and harmonic vibrational modes, and the mixture of those different vibrations depends on where you pluck it. [52.3% picked]
Why: TBA
Problem 60:
You are standing in the middle of a level subway car that is moving forward at constant velocity when another passenger accidentally spills an enormous container of olive oil. Suddenly, the floor cannot exert any frictional forces on your feet. Because nothing else is touching you, you
(A) remain in the middle of the subway car. [92.3% picked]
(B) shift toward the front of the subway car (in the direction of its velocity). [0.0% picked]
(C) shift toward the side of the subway car (perpendicular to the direction of its velocity). [0.0% picked]
(D) shift toward the back of the subway car (opposite its velocity). [7.7% picked]
Answer: (A) remain in the middle of the subway car. [92.3% picked]
Why: TBA