Physics Exam #2

question

Can a force produce a torque when there is no lever arm? (y/n)

No
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How does the lever arm change if you decrease the angle of the force? It decreases. It increases. It stays the same.

It Decreases
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How does the lever arm change when you decrease the distance to the nut? It decreases It increases Stays the same

It decreases
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How does the force needed to turn the wrench change if you increase the lever arm? It decreases. It stays the same. It increases.

it decreases
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Dan and Sue cycle at the same speed. The tires on Dan’s bike are larger in diameter than those on Sue’s bike. Which wheels, if either, have the greater rotational speed? Dan’s wheels have the greater rotational speed. Sue’s wheels have the greater rotational speed. They have the same rotational speed.

Sues’s wheels have the greater rotational speed
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If the world’s populations moved to the North Pole and the South Pole, would the 24-hour day become longer, shorter, or stay the same? longer shorter stay the same

Shorter
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Horses that move with the fastest linear speed on a merry-go-round are located near the center. near the outside. anywhere, because they all move at the same speed.

near the outside
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Your pet hamster sits on a record player whose angular speed is constant. If he moves to a point twice as far from the center, then his linear speed halves. remains the same. doubles.

Doubles
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Since each rolling wheel of a railroad train is tapered, the narrow part of the wheel has a tangential speed that is smaller than that of the wide part. greater than that of the wide part. the same as that of the wide part.

smaller than that of the wide part
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The tapered shape of the parts of the wheels that ride on railroad tracks allows opposite wheels to in effect, vary their diameters. travel at different linear speeds for the same rotational speed. Both A and B are correct.

Both A and B are correct
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Which moves faster in m/s on a merry-go-round: a horse on the inside or a horse on the outside near the outer rail? outside horse inside horse Both move at the same speed in m/s.

Outside horse
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If a turntable’s rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will double. remain the same. halve.

Double
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Suppose the circumference of a bicycle wheel is 2 meters. If it rotates at 1 revolution per second when you are riding the bicycle, then your speed will be 3 m/s. 3.14 m/s. 6.28 m/s. 2 m/s. 1 m/s.

2 m/s
question

Consider a string with several rocks tied along its length at equally spaced intervals. You whirl the string overhead so that the rocks follow circular paths. Compared to a rock in the middle of the string, a rock at the outer end moves twice as fast. at the same linear speed. half as fast.

twice as fast
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A broom is easier to balance on its end when the heavier end (the brush end) is nearest your hand. highest, farthest from your hand. same either way

question

An industrial flywheel has a greater rotational inertia when most of its mass is uniformly spread out as in a disk. nearest the axis. nearest the rim.

nearest the rim
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A coin and a ring roll down an incline starting at the same time. The one to reach the bottom first will be the coin. ring. Both reach the bottom at the same time.

coin
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The rotational inertia of your leg is greater when your leg is straight. bent. same either way

straight
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A torque acting on an object tends to produce velocity. a center of gravity. rotation. linear motion. equilibrium.

rotation
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On a balanced seesaw, a boy three times as heavy as his partner sits more than 1/3 the distance from the fulcrum. 1/3 the distance from the fulcrum. less than 1/3 the distance from the fulcrum.

1/3 the distance from the fulcrum
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Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you’ll multiply the torque by two. four. eight.

two
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The famous Leaning Tower of Pisa doesn’t topple over because its center of gravity is displaced from its center. relatively low for such a tall building. stabilized by its structure. in the same place as its center of mass. above a place of support.

above a place of support
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The center of gravity of a circular disk of sheet metal is midway between the center and the outside. two-thirds of the way between the center and the outside. at the center of the disk. impossible to predict without knowing the metal density.

at the center of the disk
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For a system in mechanical equilibrium the resultant forces and torques must be equal. the resultant torques must be zero. the resultant forces and torques must both be zero. the resultant force must be zero.

the resultant forces and torques must both be zero
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To turn a stubborn screw, it is best to use a screwdriver that has a wide handle. long handle. smooth handle. none of these

wide handle
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A 1-kg rock is suspended from the tip of a meter stick at the 0-cm mark so that the meter stick balances like a seesaw when the fulcrum is at the 25-cm mark. From this information, what is the mass of the meter stick? 1/4 kg 3/4 kg more than 1 kg 1 kg 1/2 kg

1 kg
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A ball rolls down a hill mainly because of its angular acceleration. its angular momentum. an unbalanced torque. a balanced torque. its rotational inertia.

an unbalances torque
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If the Earth rotated more slowly about its axis, your apparent weight would decrease. be zero. stay the same. increase.

increase
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Suppose you are at the center of a large freely-rotating horizontal turntable in a carnival funhouse. As you crawl toward the edge, the angular momentum of you and the turntable remains the same, but the RPMs decrease. decreases. increases. decreases in direct proportion to your decrease in RPMs. none of these

remains the same, but the RPMs decrease
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Torque = Lever Arm × Force Calculate the torque produced by a 40-N perpendicular force at the end of a 0.15-m-long wrench.

τ = 6.0 Nm
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Centripetal Force: F=mv^2/r Calculate the tension in a horizontal string that whirls a 2.2-kg toy in a circle of radius 2.2 m when it moves at 3.4 m/s on an icy surface.

F= 12N
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Calculate the force of friction that keeps a 75-kg person sitting on the edge of a horizontal rotating platform when the person sits 2.0 m from the center of the platform and has a tangential speed of 3.8 m/s .

F= 540N
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Angular Momentum = mvr Calculate the angular momentum of the person if the force of friction that keeps a 75-kg person sitting on the edge of a horizontal rotating platform when the person sits 2.1 m from the center of the platform and has a tangential speed of 2.8 m/s .

L = 440 kg⋅m2/s
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If the force of friction that keeps a 90-kg person sitting on the edge of a horizontal rotating platform when the person sits 2.2 m from the center of the platform and has a tangential speed of 6.2 m/s , what will be the person’s angular momentum?

L= 1200 kg⋅m2/s
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The rock and meterstick balance at the 25-cm mark, as shown. The meterstick has a mass of 1.3 kg . What must be the mass of the rock?

1.3 kg
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To tighten a bolt, you push with a force of 78 N at the end of a wrench handle that is 0.20 m from the axis of the bolt. What torque are you exerting?

16 Nm (78 x 0.20)
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From previous answer: If you move your hand inward to be only 0.10 m from the bolt, find the force

160N
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Do your answers depend on the direction of your push relative to the direction of the wrench handle?

Yes
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If a pendulum is shortened, does its frequency increase or decrease? increase decrease does not change

increase
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What about its period? increase does not change decrease

decrease
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A bat chirps as it flies toward a wall. Is the frequency of the echoed chirps it receives higher, lower, or the same as the emitted ones? lower higher the same as the emitted ones

higher
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A railroad locomotive is at rest with its whistle shrieking, then starts moving toward you. Does the frequency of sound that you hear increase, decrease, or stay the same? decreases increases stays the same

increases
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How about the wavelength reaching your ear? increases decreases stays the same

decreases
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How about the speed of sound in the air between you and the locomotive? increases decreases stays the same

stays the same
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Like a transverse wave, a longitudinal wave has amplitude, wavelength, and speed. amplitude, frequency, and wavelength. wavelength, speed, and frequency. amplitude, frequency, and speed. amplitude, frequency, wavelength, and speed.

amplitude, frequency, wavelength, and speed
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Which of the following is not a transverse wave? radio sound light all of these none of these

sound
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The vibrations of a transverse wave move in a direction that changes with speed. along the direction of wave travel. at right angles to the direction of wave travel.

at right angles to the direction of wave travel
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Radio waves travel at the speed of light, 300,000 km/s. The wavelength of a radio wave received at 100 megahertz is 3.0 m. 300 m. 0.003 m. 30 m. none of these

3.0 m
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The frequency of a simple pendulum depends on its length. the acceleration due to gravity. its mass. all of these two of these

two of these
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An object that completes 10 vibrations in 20 seconds has a frequency of 200 hertz. 2 hertz. 0.5 hertz.

0.5 hertz (frequency = vibration/seconds)
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To say that one wave is out of phase with another is to say that the waves are of different wavelengths. of different amplitudes. out of step. of different frequencies. all of these

out of step
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A standing wave occurs when two waves overlap. the speed of the wave is zero or near zero. a wave reflects upon itself. the amplitude of a wave exceeds its wavelength.

a wave reflects upon itself
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The Doppler effect is characteristic of sound waves. water waves. light waves. all of the above choices none of the above choices

all of the above choices
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The pendulum with the greatest frequency is the pendulum with the greatest amplitude shortest amplitude. shortest length. shortest period.

shortest period
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A wave travels an average distance of 1 meter in 1 second with a frequency of 1 hertz. Its amplitude is less than 1 meter. more than 1 meter. 1 meter. not enough information to say

not enough information to say
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The frequency of the second hand on a clock is 1/60 hertz. 1 hertz. 60 hertz.

1/60 hertz
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The period of the second hand on a clock is 1/60 second. 1 second. 60 seconds. 3600 seconds. 12 hours.

60 seconds
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A Doppler effect occurs when a source of sound moves toward you. at right angles to you. both of these none of these

toward you
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Some of a wave’s energy dissipates as heat. In time, this will reduce the wave’s speed. amplitude. wavelength. frequency. period.

amplitude
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A wave oscillates up and down two complete cycles each second. If the wave travels an average distance of 6 meters in one second, its wavelength is 6 m. 0.5 m. 1 m. 2 m. 3 m.

3 m (6/2)
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What is the frequency, in hertz, that corresponds to each of the following periods? 0.10 s

10 Hz
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What is the frequency, in hertz, that corresponds to each of the following periods? 5.0 s

0.20 Hz
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What is the frequency, in hertz, that corresponds to each of the following periods? 1/60 s

60 Hz
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What is the period, in seconds, that corresponds to each of the following frequencies? 10 Hz

0.10 s
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What is the period, in seconds, that corresponds to each of the following frequencies? 0.2 Hz

5.0 s
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What is the period, in seconds, that corresponds to each of the following frequencies? 60 hz

1.7×10^-2 s
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A weight suspended from a spring is seen to bob up and down over a distance of 30 cm twice each second. what is its frequency?

2.0 Hz
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A weight suspended from a spring is seen to bob up and down over a distance of 30 cm twice each second. what is its period?

0.50 s
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A weight suspended from a spring is seen to bob up and down over a distance of 30 cm twice each second. what is its amplitude?

15 cm
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How many nodes, not including the endpoints, are there in a standing wave that is two wavelengths long?

3
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Three wavelengths long?

5
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A bat flying in a cave emits a sound and receives its echo 0.10 s later. Find its distance from the cave wall

d= 17m
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Imagine a Rip van Winkle type who lives in the mountains. Just before going to sleep, he yells, \”WAKE UP\”, and the sound echoes off the nearest mountain and returns 7.2 hours later. Find the distance between Rip and the imaginary mountain

d= 4400km
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A grunting porpoise emits sound at 57 Hz . What is the wavelength of this sound in water, where the speed of sound is 1500 m/s?

26 m
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A piano tuner knows that a key on the piano is tuned to the frequency of his tuning fork when he strikes them at the same time and the number of beats he hears each second is 2. 4. 1. 0. 3.

question

A general rule for estimating the distance in kilometers between an observer and a lightning bolt is to count the number of seconds between seeing the lightning and hearing it, and dividing by 4. 5. 3. 2. none of these

3
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The beat frequency produced when a 240 hertz tuning fork and a 246 hertz tuning fork are sounded together is 6 hertz. 240 hertz. 245 hertz. 12 hertz. None of the above choices are correct.

6 hertz
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Inhaling helium increases the pitch of your voice. One reason for this is that sound travels slower in helium than in air. faster in helium than in air. the same speed in helium, but the wavelength is greater.

faster in helium than in air
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Resonance can be looked at as forced vibration with the maximum amount of energy input. least amount of energy input. minimum beat frequency. matching of wave amplitudes. matching of constructive and destructive interference.

least amount of energy input
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When the handle of a tuning fork is held solidly against a table, the sound becomes louder and the time that the fork keeps vibrating becomes shorter. becomes longer. remains the same.

becomes shorter
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A 340-hertz sound wave travels at 340 m/s in air with a wavelength of 10 m. 1 m. 1000 m. 100 m. None of the above choices are correct.

1m
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For AM radio, the A stands for almost. agony. amplitude. authorized. acceleration.

amplitude
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Which doesn’t belong to the same family? infrasonic waves longitudinal waves ultrasonic waves radio waves shock waves

question

Sound waves can interfere with one another so that no sound results. False True Either true or false, depending on the air temperature.

True
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Caruso is said to have made a crystal chandelier shatter with his voice. This is a demonstration of beats. sound refraction. an echo. resonance. interference.

Resonance
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The object with the highest natural frequency is a small bell. large bell. medium size bell.

small bell
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The energy of sound in air eventually becomes increased internal energy of the air. cancelled by destructive interference. weaker and weaker until it disappears. cancelled by both destructive and constructive interference.

increased internal energy of the air
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When the speed of sound near the ground is greater than it is at higher altitudes, the sound tends to be bent to the right. to the left. upward. downward. None of the above choices are correct.

upward
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Sound travels faster in steel. a vacuum. air. water. Sound travels at about the same speed in all of the above media.

steel
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The approximate range of human hearing is 40 hertz to 40,000 hertz. 10 hertz to 10,000 hertz. 20 hertz to 20,000 hertz. Actually all of these – depends on the hearing ability of the person.

20 hertz to 20,000 hertz
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The source of every sound is something that is a net emitter of energy. vibrating. moving. undergoing simple harmonic motion. accelerating.

vibrating
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You watch distant Sally Homemaker driving nails into a front porch at a regular rate of 1 stroke per second. You hear the sound of the blows exactly synchronized with the blows you see. And then you hear one more blow after you see the hammering stop. Calculate the distance of sally from you

d= 340m
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What is the wavelength of a 310-Hz tone in air?

λ = 1.1 m
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What is the wavelength of a 31000-Hz ultrasonic wave in air?

λ = 1.1×10^−2 m
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An oceanic depth-sounding vessel surveys the ocean bottom with ultrasonic waves that travel 1530 m/s in sea-water. The time delay of the echo to the ocean floor and back is 5.75 s . Find the depth of the water directly below the vessel

h= 4400m
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What beat frequencies are possible with tuning forks of frequencies 258, 263, and 267 Hz ?

f1,f2,f3 = 4,5,9 Hz
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Double the frequency of sound and you also double its speed. amplitude. wavelength. all of these none of these

None of these
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We are best at hearing both infrasonic and ultrasonic sounds. infrasonic sound. ultrasonic sound. None of the above choices are true.

None of the above choices are true
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The speed of a sound wave in air depends on its wavelength. its frequency. the air temperature. All of the above choices are correct. None of the above choices are correct.

the air temperature
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The explanation for refraction must involve a change in wavelength. speed. frequency. All of the above choices are true. None of the above choices are true.

speed
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The frequencies of sound that carry farther in air are low. high. ultrasonic.

low
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The wavelengths of sound that carry farther in air are relatively long. short. ultrasonic.

long
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Longitudinal waves of different lengths are traveling though a long metal rod. Those that travel at the greatest speed are the shortest. impossible to predict without knowing the type of metal. the longest. those of medium length. None of the above choices are correct.

None of the above choices are correct
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Suppose you sound a 1056-hertz tuning fork at the same time you strike a note on the piano and hear 2 beats/second. You tighten the piano string very slightly and now hear 3 beats/second. What is the frequency of the piano string? 1054 hertz 1053 hertz 1059 hertz 1058 hertz 1056 hertz

1059 Hertz
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What causes an atom to become positively charged? Protons were added. Electrons were removed. Either protons were added, or electrons were removed. Electrons were added.

electrons were removed
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If the atoms of one object (initially neutral) have electrons rubbed off through friction with a second object, the first object becomes ________. neutral in charge negatively charged positively charged It’s impossible to say.

positively charged
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The basic reason why things become electrically charged is that the atoms (or molecules) of some materials hold on to their _______ better than those of other materials.

electrons
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If the distance between two charged objects is doubled, the resulting electric force on each object __________. increases by a factor of 2 increases by a factor of 4 decreases by a factor of 4 decreases by a factor of 2

decreases by a factor of 4
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What is the main difference between a conductor, such as copper, and an insulator, such as plastic? Conductors are charged, and insulators are neutral. Some electrons in conductors are weakly attached to the atoms, and all electrons in insulators are strongly attached to the atoms. Conductors have more excess electrons than insulators.

some electrons in conductors are weakly attached to the atoms, and all electrons in insulators are strongly attached to the atoms
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As in the video, we apply a charge +Q to the half-shell that carries the electroscope. This time, we also apply a charge -Q to the other half-shell. When we bring the two halves together, we observe that the electroscope discharges, just as in the video. What does the electroscope needle do when you separate the two half-shells again? It deflects less than it did at the end of the video. It deflects the same amount as at end of the video. It does not deflect at all. It deflects more than it did at the end of the video.

It does not deflect at all
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A glass marble is rubbed against a piece of silk. As a result the piece of fabric acquires extra electrons. What happens to the glass marble? Check all that apply. The marble has lost the same number of electrons acquired by the piece of silk. The marble has acquired the same number of electrons acquired by the piece of silk. The marble acquires a positive charge and repels the piece of silk. The marble acquires a positive charge and attracts the piece of silk. The marble acquires a negative charge and attracts the piece of silk. The marble acquires a negative charge and repels the piece of silk.

-the marble has lost the same number of electrons acquired by the piece of silk -the marble acquires a positive charge and attracts the piece of silk
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Two glass marbles (1 and 2), each supported by a nylon thread, are rubbed against a piece of silk and then are placed near a third glass marble (3), also supported by a similar thread. Assuming that marble 3 has not been in contact with the piece of fabric, which of the following statements best describes the situation when the three marbles are brought together? To keep things simple in this Tutorial, we will ignore the effects of polarization and just focus on the overall charge of each object. Marbles 1 and 2 attract each other, but no interaction occurs with marble 3. Both marbles 1 and 2 attract marble 3. The three marbles will repel each other. Marbles 1 and 2 repel each other, but no interaction occurs with marble 3.

marbles 1 and 2 repel each other, but no interaction occurs with marble 3
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An electron volt, eV, is a unit of energy. Which is larger, a GeV or a MeV? GeV MeV

GeV
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What would happen to the two balls if one of them were kept positively charged and the charge on the other ball were slowly increased, making it more and more positive? The balls would not move relative to each other. The balls would begin to move farther apart. The balls would begin to move closer together.

the balls would begin to move farther apart
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What would happen to the two balls if one of them were kept positively charged and the charge on the other ball were slowly made increasingly negative? The balls would begin to move farther apart. The balls would begin to move closer together. The balls would not move relative to each other.

the balls would begin to move closer together
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What would happen to the two balls if both of them had a non-neutral charge and you slowly increased the mass of the balls? The angle of the balls with respect to the vertical would not change. The angle of the balls with respect to the vertical would increase. The angle of the balls with respect to the vertical would decrease.

the angle of the balls with respect to the vertical would decrease
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Two conducting spheres are each given a charge Q. The radius of the larger sphere is three times greater than that of the smaller sphere. If the electric field just outside of the smaller sphere is E0, then the electric field just outside of the larger sphere is 3 E0 1/3 E0 1/9 E0 E0 9 E0

1/9 E0
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To see why, calculate and compare the gravitational and electrical forces between an electron and a proton separated by 10−10m. The charges and masses are given in the textbook.

Felec/Fgrav = 2⋅10^39
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Two point charges are separated by 6.0 cm . The attractive force between them is 22 N . Suppose that the charges attracting each other have equal magnitude. Rearrange Coulomb’s law and find the magnitude of each charge.

Q = 3.0×10^−6 C
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Two pellets, each with a charge of 0.70 microcoulomb (7.0×10−7 C ), are located 2.4 cm (2.4×10−2 m ) apart. Find the electric force between them.

F= 7.7 N
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What would be the mass of an object that would experience this same force in Earth’s gravitational field?

m = 0.77 kg
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A droplet of ink in an industrial ink-jet printer carries a charge of 2.1×10−10 C and is deflected onto paper by a force of 2.9×10−4 N . Find the strength of the electric field to produce this force

E = 1.4×10^6 Vm
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The potential difference between a storm cloud and the ground is 100 million V. If a charge of 1.4 C flashes in a bolt from cloud to Earth, what is the change of potential energy of the charge?

E = 1.4×10^8 J
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An energy of 0.12 J is stored in the metal sphere on top of a Van de Graaff generator. A spark carrying 0.50 micro-coulomb (5.0×10−7 C ) discharges the sphere. Find the sphere’s potential relative to ground.

V = 2.4×10^5 V
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If a drop of mass 1.2×10−14kg remains stationary in an electric field of 3.675×105N/C, what is the charge of this drop?

Q = 3.2×10^−19 C
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How many extra electrons are on this particular oil drop (given the presently known charge of the electron)?

N = 2 electrons
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The unit of electric charge, the coulomb, is the charge on one electron. a specific number of neutrons. a specific large number of electrons. a neutron. a quark.

a specific large number of electrons
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The primary purpose of a lightning rod is to attract lightning and guide it to the ground. induce a charge opposite to that of charged clouds overhead. cancel the electric field within the structure to which it is attached. discharge the structure to which it is attached.

discharge the structure to which it is attached
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To say that an object is electrically polarized is to say its internal electric field is zero. it is only partially conducting. its charges have been rearranged. it is electrically charged. it is to some degree magnetic.

its charges have been rearranged
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A balloon will stick to a wooden wall if the balloon is charged negatively. positively. either positively or negatively. None of the above choices are correct.

either positively or negatively
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Particle A has twice the charge of nearby particle B. Compared to the force on Particle A, the force on Particle B is twice as much. four times as much. the same. half as much. None of the above choices are correct.

the same
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A conductor differs from an insulator in that a conductor has faster moving molecules. has more electrons than protons. has more energy than an insulator. has more protons than electrons. none of these

none of these
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A negatively charged rod is held near a metal can that rests on a dry wood table. If you touch the opposite side of the can momentarily with your finger, the can is then discharged only on the side touched. completely discharged. partially discharged. negatively charged. positively charged.

positively charged
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The direction of an electric field is the direction of the force that the field would exert on an electron. an atom. a proton. a neutral test charge. a molecule.

a proton
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The electric field around an isolated electron has a certain strength 1 cm from the electron. The electric field strength 2 cm from the electron is the same. twice as much. half as much. four times as much. None of the above choices are correct.

None of the above choices are correct
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Charge carriers in a metal are electrons rather than protons because electrons are loosely bound. smaller. negative. all of these none of these

loosely bound
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In the unlikely case of a lightning strike, it is worse to be inside a building framed with iron. steel. aluminum. wood.

wood
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Two charges separated by one meter exert 1-N forces on each other. If the charges are pushed to 1/4 meter separation, the force on each charge will be 8 N. 2 N. 16 N. 1 N. 4 N.

16 N
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Two charges separated by one meter exert 1-N forces on each other. If the charges are pulled to 3-m separation distance, the force on each charge will be 9 N. 0.33 N. 3 N. 0.11 N. 0 N.

0.11 N
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Two charged particles attract each other with a force F. If the charges of both particles are doubled, and the distance between them also doubled, then the force of attraction will be F. F/2. 2 F. F/4. none of these

F
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Two charged particles repel each other with a force F. If the charge of one of the particles is doubled and the distance between them is also doubled, then the force will be F. F/4. 2 F. F/2. none of these

F/2
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Which force binds atoms together to form molecules? gravitational electrical nuclear centripetal none of these

electrical
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In an electrically neutral atom the number of protons in the nucleus is equal to the number of neutrons in the nucleus. electrons that surround the nucleus. Choices A and B are both correct. Choices A and B are both incorrect.

electrons that surround the nucleus
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Strip electrons from an atom and the atom becomes a molecule. positive ion. different element. negative ion.

positive ion
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The electrical force between charges is strongest when the charges are close together. far apart. The electric force is constant everywhere.

close together
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An electron and a proton repel each other. neither attract nor repel each other. attract each other.

attract each other
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Two protons attract each other gravitationally and repel each other electrically. By far the greater force is the gravitational attraction. the electrical repulsion. neither – the forces are the same.

the electrical repulsion
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A difference between electric forces and gravitational forces is that gravitational forces are not affected by the inverse-square law. separation distance. repulsive interaction. infinite range. None of the above choices are correct.

repulsive interaction
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angular velocity, w

numbers of revolution per second
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center of mass

average position of all the mass that makes up the body.
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center of gravity

the average position of weights distribution
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linear momentum

p=mv
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angular momentum

=lw
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vibrating

anything that moves back and forth, side to side, in and out, or up and down is vibrating
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mechanical wave

a periodic change both in space and time
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longitudinal waves

the direction of motion (to and fro) of the medium is parallel to the wave propagation direction
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transverse waves

the motion of the medium is perpendicular to the direction of the wave
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wave interference

The overlapping of waves of the same frequency can form the interference phenomenon resulting an increase, decrease or no-effect to the medium.
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standing waves

When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, stable regions of constructive and destructive interference are produced
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Nodes

Nodes are the regions of minimal or zero displacement
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antinodes

the regions of maximum displacement
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sounds

waves produced by the vibrations of matter
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pitch

person’s subjective impression about the frequency
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normal sound frequency range

20-20,000 Hz
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echo

reflection of sound
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refraction