Physics Exam 3 Quiz Questions

Two spheres are made of the same metal and have the same radius, but one is hollow and the other is solid. The spheres are taken through the same temperature increase. Which sphere extends more?

They expand by the same amount

You observe two helium balloons floating next to each other at the ends of strings secured to a table. The facing surfaces of the balloons are separated by 1-2 cm. You blow through the opening between the balloons. What happens to the balloons?

They move toward each other

Why doesn't the melting of ocean-based ice raise as much concern as the melting of land-based ice?

Unlike land-based ice, ocean-based ice already displaces water, so when it melts ocean levels won't change much

Stars A and B have the same radius, but star A has twice the absolute temperature and radius of star B. What is the ratio of star A's power output to star B's output due to electromagnetic radiation?

16

When an object moving in simple harmonic motion is at its maximum displacement from equilibrium, what is at a maximum?

Acceleration

When a sealed Thermos bottle full of hot coffee is shaken, what changes, if any, take place in (a) the temperature of the coffee and (b) its internal energy?

Although no energy is transferred into or out of the system by heat, work is done on the system as the result of the agitation. Consequently, both the temperature and the internal energy of the coffee increase.

Suppose you have 1 cm³ of gold, 2 cm³ of silver, and 6 cm³ of aluminum. Rank them by mass from smallest to largest.

Aluminum < Gold < Silver

On a very hot day, it's possible to cook an egg on the hood of a car. Would you select a black car or a white car on which to cook your egg?

Black; The black car absorbs more of the incoming energy from the Sun than does the white car, making it more likely to cook the egg.

The figure below shows aerial views from directly above two dams. Both dams are equally long (the vertical dimension in the diagram) and equally deep (into the page in the diagram). The dam on the left holds back a very large lake, while the dam on the right holds back a narrow river. Which dam has to be built more strongly?

Both have the same strength.

A soft drink bottle resonates as air is blown across its top. What happens to the resonant frequency as the level of fluid in the bottle decreases?

Consider the level of fluid in the bottle to be adjusted so that the air column above it resonates at the first harmonic. This is given by f = v/4L. This equation indicates that as the length L of the column increases (fluid level decreases), the resonant frequency decreases.

Concrete has a higher specific heat than does soil. Would you expect evening breezes to blow from city to country or from country to city?

Country to city The heated air in a city rises to be replaced by cooler air drawn in from the countryside. Thus, evening breezes tend to blow from country to city.

What happens to the speed if you fill the hose with water?

Decreases

Several common barometers are built using a variety of fluids. For which fluid will the column of fluid in the barometer be the highest: mercury, water, ethyl alcohol, or benzene?

Ethyl Alcohol

Two objects with different sizes, masses, and temperatures are placed in thermal contact. How does energy travel?

From the object at higher temperature to the object at lower temperature

If you are asked to make a very sensitive glass thermometer, which of the following fluids would you choose: mercury, alcohol, gasoline, or glycerin?

Gasoline

If you quickly plunge a room-temperature mercury thermometer into very hot water, what will happen to the mercury level?

Go down briefly before reaching a final reading

The period of a simple pendulum is measured to be T on the Earth. If the same pendulum were set in motion on the Moon, how would its period compare to T?

Greater than T

Blood pressure is normally measured with the cuff of the sphygmomanometer around the arm. Suppose the blood pressure is measured with the cuff around the calf of the leg of a standing person. How would the readings of the blood pressure compare?

Greater than it is for the arm

One container is filled with argon gas and the other with helium gas. Both containers are at the same temperature. Which atoms have the higher RMS speed?

Helium

A window air conditioner is placed on a table inside a well-insulated apartment, plugged in and turned on. What happens to the average temperature of the apartment?

It increases.

A thermodynamic process occurs in which the entropy of a system changes by −6 J/K. According to the second law of thermodynamics, what can you conclude about the entropy change of the environment?

It must be +6 J/K or more.

You are tuning a guitar by comparing the sound of the string with that of a standard tuning fork. You notice a beat frequency of 5 Hz when both sounds are present. As you tighten the guitar string, the beat frequency rises steadily to 8 Hz. What should you do to tune the string exactly to the tuning fork?

Loosen the String

Are the kinetic and potential energies at a given point in the object-spring system motion affected by the change in mass? Explain

No E = 1/2 kA2 changing the mass has no effect on total energy

Objects deep beneath the surface of the ocean are subjected to extremely high pressures. Some bacteria in these environments have adapted to pressures as much as a thousand times atmospheric. How might these bacteria be affected if they were rapidly moved to the surface of the ocean?

One can think of each bacterium as being a small bag of liquid containing bubbles of gas at a very high pressure. If the bacterium is raised rapidly to the surface, the ideal gas law indicates that the volume must increase dramatically. In fact, this increase in volume is sufficient to rupture the cell.

Two rods of the same length and diameter are made from different materials. The rods are to connect two regions of different temperatures so that energy will transfer through the rods by heat. Is the rate of energy transfer by heat larger when positioned in series (_ _) or in parallel (=)?

Parallel

A simple pendulum is suspended from the ceiling of a stationary elevator, and the period is measured. If the elevator moves with constant velocity, what happens to the period? If the elevator accelerates upward, what happens to the period?

Remain the same; Decrease

If a grandfather clock were running slow, how could we adjust the length of the pendulum to correct the time?

Shorten the pendulum to decrease the period between ticks.

A pendulum clock depends on the period of a pendulum to keep correct time. Suppose a pendulum clock is keeping correct time and then Dennis the Menace slides the bob of the pendulum downward on the oscillating rod. How does the clock run?

Slow

In winter, why did pioneers store an open barrel of water alongside their produce?

The high heat capacity of the barrel and water and its high heat of fusion mean that a large amount of heat would have to leak out of the cellar before the water and produce froze solid. Evaporation of the water keeps the relative humidity high to protect foodstuffs from drying out.

Concrete has a higher specific heat than does soil. Use this fact to explain (partially) why a city has a higher average temperature than the surrounding countryside.

The large amount of energy stored in the concrete during the day as the sun falls on it is released at night, resulting in an overall higher average temperature than the countryside.

A rubber balloon is blown up and the end tied. Is the pressure inside the balloon greater than, less than, or equal to the ambient atmospheric pressure? Explain.

The pressure inside the balloon is greater than the ambient atmospheric pressure because the pressure inside must not only resist the external pressure, but also the force exerted by the elastic material of the balloon.

A crude model of the human throat is that of a pipe open at both ends with a vibrating source to introduce the sound into the pipe at one end. Assuming the vibrating source produces a range of frequencies, discuss the effect of changing the pipe's length.

The resonant frequency depends on the length of the pipe. Thus, changing the length of the pipe will cause different frequencies to be emphasized in the resulting sound.

How long will an ice cube wrapped in a wool blanket remain frozen than an identical ice cube exposed to air at room temperature?

a longer time than an identical ice cube exposed to air at room temperature

A person shakes a sealed, insulated bottle containing coffee for a few minutes. What is the change in the temperature of the coffee?

a slight increase

Identify path B as isobaric, isothermal, isovolumetric, or adiabatic

adiabatic

One of the predicted problems due to global warming is that ice in the polar ice caps will melt and raise sea level everywhere in the world. Where is this problem the most worrisome?

at the south pole, where most of the ice sits on land

Suppose you are throwing two dice in a game of craps. For any given throw, the 2 numbers that are faceup can have a sum of any number from 2-12. Which outcome is most probable? Which is least probable?

most probable: 7 least probable: 2 or 12

Stars A and B have the same temperature, but star A has twice the radius of star B. What is the ratio of star A's power output to star B's output due to electromagnetic radiation? The emissivity of both stars can be assumed to be 1.

4

What is the ratio if star A has both twice the radius and twice the absolute temperature of star B?

64

An object of mass m is attached to a horizontal spring, stretched to a displacement A from equilibrium and released, undergoing harmonic oscillations on a frictionless surface with period T0. The experiment is then repeated with a mass of 4m. What is the new period of oscillation?

2T0

Which of the following frequencies are higher harmonics of a string with fundamental frequency of 150 Hz?

300 Hz & 600 Hz

A block on the end of a horizontal spring is pulled from equilibrium at x=0 to x=A and released. Through what total distance does it travel in one full cycle of its motion?

4A

Star A has twice the radius and twice the absolute temperature of star B. What is the ratio of the power output of star A to that of star B? The emissivity of both stars can be assumed to be 1.

64

A steam-driven turbine is one major component of an electric power plant. Why is it advantageous to increase the temperature of the steam as much as possible?

A higher steam temperature means that more energy can be extracted from the steam. For a constant temperature heat sink at Tc and steam at Th, the maximum efficiency of the power plant goes as (Th − Tc) / (Th) = 1 − (Tc / Th) and is maximized for high Th.

Why does a vibrating guitar string sound louder when placed on the instrument than it would if allowed to vibrate in the air while off the instrument?

A vibrating string is not able to set very much air into motion when vibrated alone. Thus it will not be very loud. If it is placed on the instrument, however, the string's vibration sets the sounding board of the guitar into vibration. A vibrating piece of wood is able to move a lot of air, and the note is louder.

Calculate the slopes for the A, C, and E portions of the figure. Rank the slopes from least to greatest and explain what your ranking means.

C < A < E Larger specific heats result in a smaller slope; more energy is required to achieve a given temperature change

Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are as follows: Engine A: Th= 1000 K, Tc= 700 Engine B: Th= 800 K, Tc= 500 Engine C: Th=600 K, Tc= 300 K Rank the engines in order of their theoretically possible efficiency from highest to lowest

C > B > A

As an airplane flying with constant velocity moves from a cold air mass into a warm air mass, what happens to the Mach number?

Decrease

The density of lead is greater than iron, and both metals are denser than water. How does the buoyant force on a solid lead object compare to that of the buoyant force acting on a solid iron object of the same dimensions?

Equal buoyant forces

Balboa Park in San Diego has an outdoor organ. When the air temperature increases, what happens to the fundamental frequency of the organ pipes?

Increases

If you stretch a rubber hose and pluck it, you can observe a pulse traveling up and down the hose. What happens to the speed of the pulse if you stretch the hose more tightly?

Increases

You need to pick up a very hot cooking pot in your kitchen. You have a pair of hot pads. Should you soak them in cold water or keep them dry in order to pick up the pot most comfortably?

Keep them dry The air pockets in the pad conduct heat slowly. Wet pads absorb some heat energy in warming up themselves, but the pot would still be hot and the water would quickly conduct and convect a lot of heat right to you.

Is it possible to construct a heat engine that creates no thermal pollution?

No Practically speaking, it isn't possible to create a heat engine that creates no thermal pollution, because there must be both a hot heat source (energy reservoir) and a cold heat sink (low-temperature energy reservoir). The heat engine will warm the cold heat sink and will cool down the heat source. If either of those two events is undesirable, then there will be thermal pollution.

Atmospheric pressure varies from day to day. How does the level of a floating ship on a high-pressure day compare to that of a low-pressure day?

No difference

If the amplitude of a system moving in simple harmonic motion is doubled, what quantity does not change?

Period

For a simple harmonic oscillator, which of the following pairs of vector quantities cannot both point in the same direction?

Position & Acceleration

Why do small planets tend to have little or no atmosphere?

The existence of an atmosphere on a planet is due to the gravitational force holding the gas of the atmosphere to the planet. On a small planet, the gravitational force is very small, and the escape speed is correspondingly small. If a small planet starts its existence with an atmosphere, the molecules of the gas will have a distribution of speeds, according to kinetic theory. Some of these molecules will have speeds higher than the escape speed of the planet and will leave the atmosphere. As the remaining atmosphere is warmed by radiation from the Sun, more molecules will attain speeds high enough to escape. As a result, the atmosphere bleeds off into space.

The first law of thermodynamics says we can't get more out of a process that we put in, but the second law says that we can't break even. Explain this statement.

The first law is a statement of conservation of energy that says that we cannot devise a cyclic process that produces more energy than we put into it. If the cyclic process takes in energy by heat and puts out work, we call the device a heat engine. In addition to the first law's limitation, the second law says that, during the operation of a heat engine, some energy must be ejected to the environment by heat. As a result, it is theoretically impossible to construct a heat engine that will work with 100% efficiency.

Suppose you're on a hot air balloon ride, carrying a buzzer that emits a sound of frequency f. If you accidentally drop the buzzer over the side while the balloon is rising at constant speed, what can you conclude about the sound you hear as the buzzer falls to the ground?

The frequency decreases, and intensity decreases

What happens to the speed of a wave on a string when the frequency is doubled? Assume that the tension in the string remains the same.

The speed of a wave on a string is given by v = √(F/μ). This says the speed is independent of the frequency of the wave. Thus, doubling the frequency leaves the speed unaffected.

A tile floor may feel uncomfortably cold to your bare feet, but a carpeted floor in an adjoining room at the same temperature feels warm. Why?

The tile is a better conductor of heat than carpet. Thus, energy is conducted away from your feet more rapidly by the tile than by the carpeted floor.

An ice cube is placed in a glass of water. What happens to the level of the water as the ice melts?

The water level on the side of the glass stays the same. The floating ice cube displaces its own weight of liquid water, and so does the liquid water into which it melts.

Older auto-focus cameras sent out a pulse of sound and measured the time interval required for the pulse to reach an object, reflect off of it, and return to be detected. Can air temperature affect the camera's focus? New cameras use a more reliable infrared system.

Yes, the camera may interpret an object as being closer than it actually is on a hot day.

By visual inspection, order the PV diagrams shown in the figure from the most negative work done on the system to the most positive work done on the system.

a < c < b < d

How does the subsequent total mechanical energy of the object with mass 4m relate to the original total mechanical energy?

equal to the original total mechanical energy

A pipe open at both ends resonates at a fundamental frequency fopen. When one end is covered and the pipe is again made to resonate, the fundamental frequency is fclosed. How do the two resonant frequencies compare?

fclosed= 1/2*fopen

A poker is a stiff, nonflammable rod used to push burning logs around in a fireplace. Suppose it is to be made of a single material. For best functionality and safety, the poker should be made from material with

high specific heat and low thermal conductivity.

What action will increase the speed of sound in air?

increasing the air temperature

Suppose you have 1 kg each of: iron, glass, and water, and all three samples are at 10°. Rank the samples from least to greatest amount of energy transferred by heat if enough energy is transferred so that each increases in temperature by 20°C.

iron < glass < water

Identify path D as isobaric, isothermal, isovolumetric, or adiabatic

isobaric

Identify path C as isobaric, isothermal, isovolumetric, or adiabatic

isothermic

Identify path A as isobaric, isothermal, isovolumetric, or adiabatic

isovolumetric

If a spring is cut in half, what happens to its spring constant?

it doubles

An object-spring system undergoes simple harmonic motion with an amplitude A. Does the total energy change if the mass is doubled but the amplitude isn't changed?

no

The pressure at the bottom of a glass filled with water (p= 1000 kg/m³) is P. The water is poured out and the glass is filled with ethyl alcohol (p= 806 kg/m³). The pressure at the bottom of the glass is now

smaller than P

Suppose you have 1 kg each of: iron, glass, and water, and all three samples are at 10°. Rank the samples from lowest to highest temperature after 100 J of energy is added to each by heat.

water < glass < iron

What is the entropy change of a system that undergoes a reversible, adiabatic process? [ΔS ? 0]

ΔS = 0