Deck 9: Resonance and Mechanical Waves

Question 1

You are a superb proposal writer and convince NASA to fund your taking a pendulum clock to Mars and studying how it runs. Compared to the time it should keep on Earth, the clock will run

A) slower.
B) faster.
C) at the same rate.
D) backwards

Answer 1

slower.

Question 2

You are a superb proposal writer and convince NASA to let you tag along to Mars with a pendulum clock in order to study gravity. Compared to how it would be on Earth, the time it takes for the pendulum to compete one cycle will be

A) shorter.
B) longer.
C) the same.
D) zero.

Answer 2

longer.

Question 3

You are working late in the physics lab, where you measure the period of a pendulum to be 0.8 s. You fall asleep and have a dream that you are on a planet whose gravitational strength is 4 times that of the earth. If your dream is to be physically accurate, the period of the pendulum in your dream must be

A) 0.8 s.
B) 0.4 s.
C) 1.6 s.
D) 3.2 s.

Answer 3

0.4 s.

Question 4

You are doing some spring cleaning and decide to clean out your house. You want to make a new window in your wall with which to see nature come to life, so you tie a heavy mass to a short string and attach the string to a beam in your ceiling so it can swing freely like a pendulum. You lift the ball and let it go for practice, and it takes exactly 0.5 s to come right back to you. Ready for the real thing, you quadruple the length of the pendulum. Were it to swing freely also, it would take ____ to return to you after you let it go.

A) 4 s.
B) 1 s
C) 0.5 s.
D) 2 s.

Question 5

What does the period of a pendulum depend on?

A) Mass and gravity.
B) Length and mass.
C) Length and gravity.
D) Mass, length and gravity.

Question 6

On a warm, balmy summer day you decide to relax by watching the latest building renovation in your neighborhood. You notice that a very heavy wrecking ball is attached to a much lighter chain and is dangling from a crane and swinging back and forth. As long as it does not swing too high the time it takes the wrecking ball to complete one full oscillation will be independent of

A) the weight of the ball, but not the amplitude of the motion.
B) both the amplitude of the motion and the weight of the ball.
C) both the length of the chain supporting the ball and the amplitude of the motion.
D) the amplitude of the motion, but not the weight of the ball.

Question 7

You decide to attend an amusement park which has a ride where you are strapped into a chair which is in turn firmly attached to a plastic cable. You are released and you bounce up and down as a harmonic oscillator-a mass on the end of spring. Next in line is somebody who weighs twice as much as you do. When the heavier person goes on the ride, you notice that

A) both of you will have the same period, regardless of how high you bounce.
B) the heavier rider will have a longer period than the lighter one.
C) the two riders will have the same period, as long as the heights of their bounces are the same.
D) the heavier rider will have a shorter period than the lighter one.

Question 8

When you get new tires installed on your car the wheels are carefully balanced by placing small weights around the outside of the rim. If one of these weights falls off, your car may vibrate violently when you drive at certain speeds. This vibration occurs for speeds at which

A) the rotation frequency of the off-balance wheel matches the frequency at which the car's suspension vibrates, allowing a resonant energy transfer between the two.
B) the rotational kinetic energy of the wheel exactly matches the translational kinetic energy of the car, allowing a resonant energy transfer between the two.
C) the vibrating wheel acts like a harmonic oscillator.
D) the amplitude of the vibrating wheel becomes large enough to overcome the inertia of the massive car.

Question 9

You decide to take your younger brother to the park for a fun afternoon. You notice that one ride is basically a seat attached to an old car spring. When a person sits on it, the spring vibrates rapidly but when in a car the spring vibrates much more slowly. This is because

A) Larger masses on a spring give lower frequencies.
B) Larger masses on a spring give shorter periods.
C) Larger masses on a spring give higher frequencies.
D) Larger masses on a spring give more kinetic energy loss.

Question 10

The reason for using a harmonic oscillator as a clock's time-keeper is so that the clock will keep accurate time even if the

A) frequency of the time-keeper's oscillation changes.
B) stiffness of the time-keeper's restoring force changes.
C) amplitude of the time-keeper's oscillation changes.
D) mass of the time-keeper's moving object changes.

Question 11

You work in a clock shop and are dealing with an irate customer whose clock you are restoring. They notice that the period of the pendulum in their clock is 2 s and they want to double it. So they insist that you replace the pendulum with one of the same dimensions but just heavier. So you do this. When you get the clock repaired, you and the customer check out the clock's period and find it to be

A) 2 s.
B) 4 s.
C) 8 s.
D) 16 s.

Question 12

You just bought an old car which you want to restore. It still drives, though, so you decide to take some friends for a ride in it and you notice that, at stop lights the car bounces up and down because the shocks are gone. They're not bad; they're gone. Anyway, later that day you take many more friends in your car. At stop lights now, you notice that the bouncing frequency will

A) be the same as when it contained fewer friends.
B) be lower than when it contained less friends.
C) be higher than when it contained less friends.
D) not occur because having more mass in the car dissipates energy.

Question 13

You have been contracted to make a clock for a prospecting team that is to go over a mountain pass. They are all chess experts and the guide has requested a very accurate clock. However, being from the "old days" he has mandated that there are to be no electronic clocks on the trip, meaning that you need to design a mechanical one. Would you pick a pendulum clock or a balance clock? Please explain.

Question 14

You have been hired to design a clock for the space shuttle. Please discuss what kind of clock you would design.

Question 15

In a famous television commercial a singer's voice is played on a speaker beside a nearby glass, which shatters when she hits a certain note in the song. Please explain.

Question 16

A harmonic oscillator is an oscillator

A) which makes musical - like sound when it moves
B) with a restoring force proportional to its displacement from equilibrium.
C) with a restoring force proportional to its speed
D) which has constant kinetic energy when in motion

Question 17

Your friend is discussing oscillators with you and makes the statement "Pendulum clocks are harmonic oscillators and work exactly like masses on springs that bounce when something is placed on them - the heavier the object the slower the oscillation (smaller period). They take kinetic energy and potential energy and switch them back and forth while keeping the sum of the two constant." Please identify three points which your friend got incorrect.

Question 18

________ supplies part of the energy to a pendulum clock, while _________ supplies most of the energy for a balance clock.

A) A spring; friction
B) A spring; gravity
C) Gravity; a spring
D) Air resistance; gravity

Question 19

Suppose you are engaged to a college physics major, and wind up thinking about your entire existence from the point of view of Newton's first law of motion. You find yourself looking at a pendulum clock, and describing it in terms of the first law; please describe what you would say about it.

Question 20

One reason for using a quartz crystal as a clock's time-keeper is so that the clock will

A) not need a battery.
B) keep accurate time even if the ambient temperature changes.
C) run forever.
D) have sliding parts that don't make noise.

Question 21

Many times in physics a typo can be embarrassing and costly. Consider the following typo sent to a press release by a clock designer that ended up costing them their job. "We have been successful in designing a balance clock with a anharmonic oscillator that gives high accuracy and low spring stress for increased clock life." Please explain why the designed lost their job.

Question 22

When you blow gently across the top of a particular soda bottle, it emits a tone. The column of air in the bottle is vibrating up and down in its fundamental mode. If you replace the air in the bottle with helium and then blow gently across the top of the bottle, it will emit

A) a higher pitched tone.
B) a tone at the same pitch as before.
C) no sound at all.
D) a lower pitched tone.

Question 23

When you blow gently across the top of a particular soda bottle, it emits a tone. The column of air in the bottle is vibrating up and down in its fundamental mode. If you replace the air in the bottle with something heavier than air (like carbon dioxide) and then blow gently across the top of the bottle, it will emit

A) a higher pitched tone.
B) a tone at the same pitch as before.
C) no sound at all.
D) a lower pitched tone.

Question 24

What bridge collapse in 1940 was due to a resonant energy transfer?

A) Verrazano Narrows Bridge
B) Tacoma Narrows Bridge
C) London Bridge
D) Wheatstone Bridge

Question 25

How are standing waves and traveling waves different?

A) A particle riding a standing wave has no motion.
B) Traveling waves have troughs and crests.
C) A particle riding a traveling wave has a nonzero average velocity perpendicular to the wave displacement.
D) A standing wave is bigger.

Question 26

The strings of a guitar vibrate at different frequencies. They have different thicknesses because

A) a thinner string has more tension than a thicker string and vibrates at a higher frequency.
B) a thicker string has more tension than a thinner string and vibrates at a higher frequency.
C) a thicker, more massive string vibrates at a lower frequency than a thinner string of the same length and tension.
D) a thinner, less massive string vibrates less frequently than a thicker string of the same length and tension.

Question 27

To improve a xylophone's appearance, the orchestra director decides to have it painted. Each xylophone bar is actually a harmonic oscillator that vibrates when struck by a wooden mallet. When bending in its fundamental mode, the bar's middle and ends move in opposite directions. Painting the bar adds mass to the bar without affecting its stiffness, so the paint will

A) not affect the pitch or sound volume of the bar.
B) raise the bar's pitch.
C) lower the bar's pitch.
D) not affect the pitch of the bar, but will reduce its sound volume.

Question 28

You are an antique hound. You buy an old xylophone and play it, making note that the bars on it act like harmonic oscillators when they are struck. You also see that the bars have become very dirty through years of use, so you thoroughly clean them. Removing the accumulation from the bars will

A) not affect their pitch or sound volume.
B) raise their pitch.
C) lower their pitch.
D) not affect their pitch, but will reduce their sound volume.

Question 29

If you blow across the top of a half full bottle of soda you can produce a clear tone. If you take a drink of soda to reduce the amount of liquid in the bottle and try this again the pitch (frequency) of the sound produced will

A) increase.
B) stay the same.
C) exactly double.
D) decrease.

Question 30

A guitar string that normally vibrates with a fundamental frequency of 110 Hz is also capable of vibrating at 330 Hz. When that higher frequency vibration occurs, the string is vibrating

A) with only one third of its normal mass.
B) with only one third of its normal amplitude of oscillation.
C) as 3 strings that are one third as long as the overall string.
D) with only one third of its normal tension.

Question 31

You are the owner of an organ with open - ended pipes. You notice, though, that one note is fairly far off from its target frequency. You take the organ apart, only to find that the one organ pipe making the bad note is closed, not open! Closing the organ pipe made the frequency of the note it produces

A) go up by an octave-its frequency will increase by a factor of 2.
B) go down by an octave-its frequency will decrease by a factor of 2.
C) stay the same.
D) go down by a fifth-its frequency will decrease by a factor of 1.5.

Question 32

Some musicians actually play the saw because it makes so many rich and interesting sounds. In class your instructor demonstrates the saw, which has a spring - like surface. The sounds it makes are indeed interesting but no pure tones are produced because the surface

A) cannot experience non-uniform accelerations (accelerations that vary from place to place).
B) creates overtones that are not integer multiples of their fundamental frequencies.
C) is not a harmonic oscillator.
D) is not uniform.

Question 33

You are holding a drinking straw in your hand so that both its ends are open to the air. When you blow air across one of those ends, the air in that straw vibrates and the straw emits a tone-its fundamental pitch. If you replace the air in the straw with carbon dioxide, which is more dense than air, the sound that the straw emits will

A) have the same pitch but will decrease in volume.
B) decrease in pitch (shift to a lower frequency).
C) increase in pitch (shift to a high frequency).
D) have the same pitch but will increase in volume.

Question 34

A fine crystal wineglass (actually made from lead-based glass) emits a long, pure tone when you flick it with your finger, while a cheap ordinary wineglass emits a "thunk" sound instead. Although you can break either wineglass with sound by choosing the right tone and making it sufficiently loud, it is easier to break the crystal wineglass because the crystal wineglass

A) is made from a weaker material and fractures more easily.
B) vibrates in response to a broader range of pitches.
C) wastes less energy as it vibrates and thus stores energy better.
D) cannot bend at all without breaking.

Question 35

What is the frequency of a vibration with period 0.02 second?

A) 0.02 Hertz
B) 0.02 second
C) 50 Hertz
D) 50 seconds

Question 36

Two tones which are one octave apart differ in frequency by a factor of

A) 4
B) 2
C) 3/2
D) 2^1/2

Question 37

What two properties of a material affect the speed of sound in the material?

A) Buoyant force and density.
B) Specific heat and density.
C) Density and volume.
D) Density and stiffness.

Question 38

Water is about 800 times as dense as air and about 15,000 times as stiff. If sound in air travels at about 760 mph., what is the speed of sound under water?

A) 176.7 mph.
B) 3268 mph.
C) 760 mph.
D) 800 mph.

Question 39

The waves produced by plucking a guitar string are

A) Toric
B) Longitudinal
C) Transverse
D) Chiral

Question 40

You are a baseball player and you own a guitar. You're happy with the way you play baseball; it's the pitch of a string on your guitar that you want to change. In fact you want to lower it. Please describe three ways in which you could accomplish your goal.

Question 41

A popular classroom demonstration consists of striking a tuning fork and putting the vibrating ends in a beaker of water. When the demo is done, a considerable amount of water splashing takes place, and the pitch of the tuning fork

A) increases because of the stiffness of the water
B) remains the same.
C) decreases because of damping.
D) increases because friction with the water heats it up.

Question 42

The qualities of a sound tone include pitch, volume and timbre (a piano middle C compared to a tuba middle C). Please list which properties of a sound wave correspond to each of the three sound qualities.

Question 43

Consider a power line that is suspended between two telephone poles. As the wind comes up power line just moves around in seemingly random shapes but for certain wind speeds the power line seems to "hold its shape", vibrating very prolifically and in certain patters. Please explain.

Question 44

You bought a violin that was nicely tuned in the music store. When you took it home where the temperature is much different than the music store, the notes were not in tune any more. Please explain.

Question 45

Suppose you become famous because you were able to develop a non - contact way of measuring tension in suspended wires. Your method would be based upon which physical insight below?

A) The frequency of a vibrating string depends on the tension in the wire, and so a frequency measurement will determine tension.
B) The velocity of a wave depends on the height of the string above the ground, and so by measuring velocity we can get the wire's shape which will tell us how tense it is.
C) Greater tension causes lower pitches and so all we have to do is to measure the pitch of the vibrating wire to get he tension.
D) Tension depends upon the wire's temperature and so we just make a temperature measurement.

Question 46

Suppose you are doing a popular demonstration where you fill many identical pop bottles up with different water levels and then get the system to make sound by either tapping on the side of the bottle or blowing across the top of it. The results of the demonstration will be that

A) Both types of pitches will increase with increasing water level.
B) The tapping pitch will decrease while the blowing pitch will increase with increasing water level.
C) The tapping pitch will increase while the blowing pitch will decrease with increasing water level.
D) Both types of pitches will decrease with increasing water level.

Question 47

How are standing waves and traveling waves similar?

A) Both waves never die out with time.
B) Both waves have nodes that move with time.
C) Neither wave can be longitudinal.
D) Both waves involve oscillation of some medium.

Question 48

Suppose you "think outside the box" and design a guitar with strings which all have the same thickness, length and density. Which of the following designing issues must you also consider?

A) The strings must be able to withstand a wide range of tensions in order to produce the notes needed.
B) The strings will vibrate too fast to make any noticeable sound.
C) The strings will now make their best sound with longitudinal waves.
D) The strings must be plucked only at certain spots along their length.

Question 49

You are at a coffee shop with a friend and have had enough caffeine that OSHA should be involved. You are talking late into the night with a friend who is a physics major and you say "I have absolutely no idea why pianos, guitars and xylophones all rely on transverse waves to make their sounds. I am going to re - construct those three instruments so they make beautiful music with longitudinal waves!" On the way home, the physics major thinks of a good reason that such instruments use only transverse waves. Please discuss what you think such a good reason may be.

Question 50

You are walking to an antique physics book sale with your friend and start talking about musical instruments. Your friend says that if we played violins and organs out in space, neither instrument could be heard because there would be nothing to oscillate any more, and no oscillation means no sound. Please comment on the physical accuracy of your friend's statement.

Question 51

For persons with hearing difficulties, it is sometimes recommended that they put their ear or even the area around their ear in contact with a table or solid surface in order to hear better. Please explain why doing such a thing could assist a person's hearing.

Question 52

Why does a tidal cycle take more than 12 hours?

A) Earth's rotation
B) The Moon orbits the Earth.
C) Earth moves around the sun.
D) Friction of water with land

Question 53

Why does the tide get so high in the Bay of Fundy?

A) The channels walls are very high.
B) The pull of the moon there is especially strong.
C) Water there has a large potential energy.
D) There is a natural resonance of water motion there.

Question 54

How does an object bobbing on a water wave move?

A) Circular motion
B) Up and down
C) Back and forth
D) Along with the wave.

Question 55

Water wave A has a larger wavelength than water wave B. Which wave travels faster?

A) A
B) B
C) Both travel at the same speed.
D) Not enough information is given to determine.

Question 56

It is a windy day and there are waves on the surface of the open ocean. The wave crests are 40 feet apart and 5 feet above the troughs as they pass a school of fish. The waves push on fish and making them accelerate. The fish do not like this jostling, so to avoid it almost completely the fish should swim

A) as fast as possible.
B) at least 5 feet below the surface of the water.
C) as close to the surface of the water as possible.
D) at least 20 feet below the surface of the water.

Question 57

In a cartoon, a bunny is surfing on a 10 foot wave crest that is rapidly approaching the shore. The wave crest travels onto the shore intact, with the bunny still on top of it, and continues to carry him across level land for the next twenty miles. This sort of thing can't happen in real life because

A) wave crests are made from local water and there is no water on land from which to build the crest.
B) friction between the moving wave crest and the land will slow the crest to a stop in about a mile.
C) the wave crest will begin to roll like a wheel once it reaches the shore and the bunny will be run over by it as it turns.
D) the bunny is in an unstable equilibrium and won't be able to stay on top of the crest for more than a mile or two.

Question 58

Panama is a narrow country that is bounded on the west by the Pacific Ocean and on the east by the Atlantic Ocean. When it is high tide on Panama's Atlantic side, it is

A) midway between high and low tides on Panama's Pacific side, but heading toward low tide.
B) low tide on Panama's Pacific side.
C) midway between high and low tides on Panama's Pacific side, but heading toward high tide.
D) high tide on Panama's Pacific side.

Question 59

The giant waves or tsunamis created by earthquakes have extremely long wavelengths. They travel

A) extremely quickly because they involve only the water near the ocean's surface.
B) extremely slowly and involve water to great depth in the ocean.
C) extremely slowly because they involve only the water near the ocean's surface.
D) extremely quickly and involve water to great depth in the ocean.

Question 60

A wave travels across the water on a lake, heading northward. As the result of this wave's passage, water on the surface of the lake

A) moves toward the north by a distance that is proportional to the amplitude (height) of the wave.
B) moves back and forth but makes no overall movement.
C) moves toward the north continuously at the speed of the wave.
D) moves toward the north by a distance equal to one wavelength of the wave.

Question 61

The tides are strongest near the equator because that is where the

A) centripetal force of the earth is strongest.
B) earth's gravity is weakest.
C) centrifugal force due to the earth's rotation is strongest.
D) tidal bulges caused by the moon are tallest.

Question 62

The Moon can create tides on the sides of the Earth closest to the Moon and farthest from it. This may seem peculiar, since there is nothing on the far side pulling the water up. Please explain.

Question 63

Suppose a water wave strikes a very large solid barrier, such as a cliff. The wave will redirect its motion through

A) Refraction
B) Interference
C) Reflection
D) Rarefaction

Question 64

Suppose you are a teacher and are trying to get the concept of interference across to your students. You are stuck at a stop light behind a car; both of you have your blinkers on and they blink with slightly different frequencies. Sometimes you notice they are on and off together and then a little later one is on while the other is off. Please explain how you could relate your traffic experience to a demonstration on wave interference.

Question 65

Dispersion is

A) the dependence of a wave's amplitude on the time it has been traveling.
B) the dependence of a wave's frequency on its amplitude.
C) The dependence of a wave's speed on its wavelength.
D) The dependence of a wave's speed on its amplitude.

Question 66

You are on your honeymoon but the only thing you can notice is that waves which strike the shore do so traveling directly towards it. This is an effect of

A) refraction, because as the water shallows the waves are bent so as to travel more directly towards the shore.
B) interference because the shore is sending out waves which straighten out the water waves.
C) friction with the shore, because all the sideways traveling momentum the wave has is removed with friction.
D) reflection, because the waves reflect off the ocean bottom and get straightened out.

Question 67

Water can support

A) traveling waves only.
B) surface waves only.
C) standing waves only.
D) traveling and standing waves.

Question 68

Please list three differences between surface water waves and bulk water waves (sound in water).