PHYS221 Final Exam

An object with mass m moves through free space with constant velocity. The magnitude of the force required to maintain this motion is equal to

zero.

Find the natural frequency of vibration of the salt molecule NaCl given its effective mass of 13.9 atomic mass units and a spring constant of 100 N/m.

~10^13 Hz

In any process, the maximum amount of heat that can be converted into mechanical energy

depends on the intake and exhaust temperatures.

In the figure below, two point sources S1 and S2, which are in phase, emit identical sound waves of wavelength 2.0 m. If L1 = 39 m and L2 = 36 m, what type of interference occurs at point P? -two orange lines with points P, L1, L2, S1, S2

destructive interference

How many nodes and antinodes are shown in the standing wave below? -looks like an infinity

three nodes and two antinodes

The intensity of a sound wave A is 100 times that of sound wave B. Relative to wave B the sound level of wave A is

+20 dB

A string is clamped at both ends and plucked so it vibrates in a standing wave between two extreme positions as shown by the dashed lines below. If the string has length L and the frequency of oscillation of the mode is f, the speed of the waves on that string is -diagram of wavelength with length L

(2/3)fL

(A) Can two force vectors of unequal magnitude sum to zero net force? (B) Can three force vectors of equal magnitude sum to zero net force?

(A) no, (B) yes

For a sound wave of frequency 440 Hz, what is the wavelength (i) in air (propagation speed, v = 3.3 * 10^2 m/s)? (ii) in water (propagation speed, v = 1.5 * 10 ^3 m/s)?

(i) 0.75 m, (ii) 3.41 m

What is the approximate period of the sound waves shown here? (The speed of sound in air is ~340 m/s.) -ruler with sound waves

0.0037 s

A point source of sound waves emits a disturbance with a power of 50 W = 50 J/s into a surrounding homogeneous medium. What is the intensity of the sound at a distance of 10 m from the source?

0.04 W/m^2

A 0.5 kg mass oscillates about the equilibrium position on a vertical spring with spring constant 10 N/m. Where is its equilibrium position measured from the unstretched spring position (without the hanging mass)?

0.49 m

A vibrating source generates a harmonic wave on a string under constant tension. If the power delivered to the string is doubled, by what factor does the amplitude change?

1.41

A ball is thrown directly downward with an initial speed of 8 m/s from a height of 30 m. After what time interval does the ball strike the ground?

1.78 s

The temperature in a furnace use to melt Aluminum is 660 oC. What is the average kinetic energy of the air molecules in the furnace?

1.93*10^-20 J

A sound wave has a sound β = 50 dB. Recall that β = 10 log( I/I^0) = 10 log( I/(10^-12W/m^2)). The intensity I of this wave, in W/m^2, is therefore

10^-7

A 1 kg block of aluminum is heated at atmospheric pressure such that its temperature increases from 22 oC to 40 oC. What is the change in the internal energy (in J) of the block of aluminum? The specific heat of aluminum is 9*102 J/(kg K). Enter an integer.

16200

A tube with two open ends is 1 m long. What is the wavelength of the fundamental vibration of an air column in this tube?

2 m

If you double the radiating surface area of a star while keeping its temperature constant, its power output increases by a factor of

2.

An ideal reversible engine takes in 5 kJ of energy via heat transferred in from a 500 K burner and exhausts heat at 300 K during each closed cycle in the PV plane. The amount of heat exhausted at 300 K each cycle is

3 kJ

Pure sound notes from two sources make the molecule of air at a location vibrate simple harmonically in accordance with the equations Y1 = 0.008sin(604πt) and Y2 = 0.007sin(610πt), respectively. The number of beats heard by a person at the location will be

3.

A standing wave is established on a 1.2 m long string fixed at both ends. The string vibrates in four segments when driven at 120 Hz. What is the fundamental frequency?

30 Hz

The temperature on a nice summer day is 84 oF. What is the temperature on the absolute (Kelvin) temperature scale?

302 K

At which of the following temperatures would molecules have twice the average kinetic energy they have at room temperature, 20 degrees C

313 degrees C

An object emits a sound at a frequency of 160 Hz. If the wavelength of the sound in air is measured to be 2.0 m, what is the speed of the sound wave in air under the given atmospheric conditions?

320 m/s

Suppose you have a tube 0.25 m long with a speaker at one end and with the other end open. If you gradually increase the frequency of the speaker from zero at about what approximate frequency will you hear the first resonance?

350 Hz

Data: cice = 0.50 cal/(g oC) , cwater = 1.00 cal/(g oC), csteam = 0.48 cal/(g oC), L(ice-water) = 80 cal/g , L(water-steam) = 540 cal/g How much heat is given off if 0.5 kg of steam at 373 K is converted into ice at 273 K?

360 kcal

How much heat is given off if 0.5 kg of steam at 373 K is converted into ice at 273 K?

360 kcal

A stationary source S generates circular outgoing waves on a lake. The wave speed is 5.0 m/s and the crest-to-crest distance is 2.0 m. A person in a motorboat heads directly toward S at 3.0 m/s. To this person, the frequency of these waves is:

4 Hz

A piano tuner detects 3 beats per second when she is tuning a string to a tuning fork of frequency 440 Hz. When she tightens the string, which increases the frequency of the string, the frequency of the beats initially goes down, and as she keeps increasing the frequency of the beats starts to increase. What was the original frequency of the string?

437 Hz

A piano tuner detects 3 beats per second when she is tuning a string to a tuning fork of frequency 440 Hz. When she tightens the string, which increases the frequency of the string, the frequency of the beats starts to increase. What was the original frequency of the string?

437 Hz

How much heat must be removed from a 200 g block of copper to lower its temperature from 120 oC to 60 oC? The specific heat of copper is 386 J/(kg*K).

4632 K

In the cyclic process on an ideal gas shown in the adjoining PV diagram, what is the net work done by the gas during the cycle? -graph with 3P, P, 3V, V

4PV

A box with a total surface area of 1.2 m2 and a wall thickness of 4 cm is made of an insulating material. A 10 W electric heater inside the box maintains the inside temperature at 15 oC above the outside temperature. What is the thermal conductivity of the insulating material in units of kcal/(s*oC*m)?

5.3*10^-6

A box with a total surface area of 1.2 m^2 and a wall thickness of 4 cm is made of an insulating material. A 10 W electric heater inside the box maintains the inside temperature at 15 oC above the outside temperature. What is the thermal conductivity of the insulating material in units of kcal/(s*oC*m)?

5.3*10^-6

How much heat must be added to 0.1 kg of water at 60oC to completely convert it into steam? The latent heat of vaporization is 540 kcal/kg.

58 kcal

Beats are produced when two tuning forks, one of frequency 240 Hz and another of 246 Hz are sounded together. The frequency of the beats is

6 Hz.

By how much does the entropy of 100 g of water at 100 oC change if the water is very slowly converted into steam at 100 oC? The latent heat of vaporization of water is 540 kcal/kg = 2260 kJ/kg.

606 J/K

Ethyl alcohol boils at 172 oF. What is Celsius equivalent of this temperature?

78 oC

An alarm clock makes a sound that has intensity 60 dB at a distance of 1 m. What is the sound intensity of 100 such clocks which are all 1 m away?

80 dB

A 0.500 kg mass is attached to a spring of constant 150 N/m. A driving force F(t) = (12.0 N)cos(ωt) is applied to the mass, and the damping coefficient b is 6.00 Ns/m. What is the amplitude of the steady-state motion of ω is equal to half of the natural frequency ω0 of the system?

9.7 cm

The specific heat of aluminum is 0.215 kcal/(kgoC). A 3 kg block of aluminum is heated from 10oC to 150oC. What is the change in the internal energy (in units of kcal) of the block? Enter an integer.

90

A grandfather clock is running slow. The period of its pendulum is too long. To shorten the period and make the clock run faster, you should -image of clock

decrease the length of the pendulum.

A gas is in a container with a piston lid and is taken from thermodynamic state, 1, to a new thermodynamic state, 2, by several different paths, A, B, and C, in the P-V plane. The internal energy of the gas increases during the process. The work done by the gas is largest for path -picture of "box" on graph

A

We observe the harmonic motion of an object. Its position as a function of time shown in the graph below is given by x=1*cos(π t), where x is measured in meters and t is measured in seconds. What are the amplitude (A), and the period (T), and frequency (f) of the motion?

A: 1 m, T: 2 s, f: 0.5 Hz

Two small loudspeakers emit pure sinusoidal waves with frequency-independent amplitude that are in phase. -two speaker-like structures with point P on end

At the frequencies 1.27 kHz, 2.55 kHz, and 3.82 kHz the sound at point P is loud.

When baking a potato (white or sweet) in the oven, I find they come out much more uniformly cooked if I stick aluminum rods in the potato. (You can buy such rods in any kitchen supply store.) Why does this work?

Because the aluminum has a much higher thermal conductivity than the potato so putting the rods in brings the thermal energy into the center of the potato more quickly so it cooks more uniformly.

The total entropy of the universe is always increasing. So, when water freezes, the entropy of the water is increasing.

False

Pressure vs. volume graphs for a certain gas undergoing five different cyclic processes are shown to the right. During which cycle does the gas do the greatest positive work? -five different graph options

IV

In the figures (a), (b), (c), (d) and (e) below, S is a source of sound of real frequency f and L is a listener. The speeds of the source and the listener are equal (v) in all cases except in (e) where the source is at rest and the listener is moving with speed v (as in the other cases). There is no wind. From the statements below, pick out the wrong statement. -figure with many lines going in different directions

In this case shown in fig (d) the apparent frequency as heard by the listener is less than the real frequency of the source

A car's speed changes from 20 mph to 60 mph. By what factors does its kinetic energy change?

It will increase by a factor of 9.

An object on the end of a spring is oscillating in simple harmonic motion. If the amplitude A of oscillation is doubled, how does his affect the oscillation period T and the object's maximum speed Vmax?

T remains the same and Vmax doubles

A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance.

The KE decreases and the PE increases.

On a humid summer day, perspiration does not cool you off much. Why?

The air is almost saturated with vapor and there is almost no net evaporation.

On a humid summer day, perspiration does not cool you off much. Why?

The air is almost saturated with water vapor and there is almost no net evaporation.

A bullet is fired horizontally from a rifle on the Moon (no air, g = 1.6 m/s^2) with the initial speed V0. Assuming a level and endless ground, which statement is false?

The flight time increases as V0 increases.

A gas is in a container with a piston lid and is taken from thermodynamic state, 1, to a new thermodynamic state, 2, by several different paths, A, B, and C, in the P-V plane. The internal energy of the gas increases during the process. The internal energy change is largest for path -picture of "box" on graph

The internal energy change is the same for the three paths

You fill two identical mugs with coffee, but the coffee in one mug is at a higher temperature than that in the other mug. You place the two mugs simultaneously in a microwave oven and turn it on briefly. As a result, you add 1 Joule of thermal energy to each mug. Which mug experiences the larger increase in entropy (if any)?

The mug containing the colder coffee experiences the larger increase in entropy.

Which of the statements below is wrong?

The net force acting on the pendulum bob is F = -mgsinθ. The period increases with amplitude because this force increases faster than harmonic restoring force F = -mgθ.

A train sounding its horn is approaching an observer.

The pitch of the horn's sound relative to its normal pitch is higher.

Water is flowing smoothly through the pipe shown in the diagram. -diagram showing water flow through various size of openings

The pressure is lowest in section B.

A 200 Hz sound wave has a measured wavelength of 1.675 m. Which of the following statements are true? You can choose more than one statement.

The speed of the 200 Hz wave is ~335 m/s. The wavelength of the 400 Hz wave is ~80-85 cm.

Suppose you are spending your weekend on roller skates trying to get momentum from somewhere. Which of the following will give you momentum in the north direction?

Throwing your keys southward.

Data: cice = 0.50 cal/(g oC) , cwater = 1.00 cal/(g oC), csteam = 0.48 cal/(g oC), L(ice-water) = 80 cal/g , L(water-steam) = 540 cal/g Which requires the most energy?

Vaporize 0.5 gram of water at T = 100 oC

Data: Cice = 0.50 cal/(g oC) , Cwater = 1.00 cal/(g oC), Csteam = 0.48 cal/(g oC), L(ice-water) = 80 cal/g , L(water-steam) = 540 cal/g Which requires the most energy?

Vaporize 0.5 gram of water at T = 100 oC.

Can an object's velocity change direction when its acceleration is constant?

Yes, this is possible, and a rock thrown straight up is an example.

The Doppler effect is characteristic of

all of the above choices.

The illustration shows a thermometer that uses a column of liquid to measure air temperature. In thermal equilibrium, this thermometer measures the temperature of -image of thermometer

all of the above.

A star with a surface temperature of 6000 K appears yellow in color. A star with a surface temperature of 4000 K will

appear reddish in color.

The P-V diagram below shows six curved paths (connected by vertical paths) that can be followed by a gas. Which two of them should be part of a closed cycle if the net work done by the gas is to be at its maximum positive value? -diagram with P as Y and V as X

c and e

Living cells constitute a low entropy state of matter. Living cells

can exist because they help increase the entropy of the rest of the universe

In the figure, student a has a mass of 95 kg and student b has a mass of 77 kg. They sit in identical office chairs facing each other. Student a places his bare feet on the knees of student b, as shown. Student a then suddenly pushes outward with his feet, causing both chairs to move. During the push, and while the students are still touching one another -diagram showing the two students

each student exerts the same amount of force on the other.

A car travels over a dirt road that contains a series of equally spaced bumps (a so-called "washboard" road). While traveling at a given speed, the driver experiences a very jarring ride. When the driver drives at a higher speed, however, the ride gets smoother. That is because

going faster in the car forces the suspension to oscillate at a frequency higher than its natural frequency.

A sample of low-density gas is initially at room temperature and has pressure P0. The gas is warmed at constant volume until the pressure is 2P0. Compared to the initial Celsius temperature of the gas, the final Celsius temperature is

greater by a factor of more than 2

A heat engine extracts usable work by permitting

heat to flow from a hotter object to a colder object.

A man, with his arms at his sides, is spinning on a light frictionless turntable. When he extends his arms

his angular momentum remains the same.

In a mixture of hydrogen, oxygen, and nitrogen gases at a given temperature, the molecules having the greatest average speed are those of

hydrogen.

In any process, the maximum amount of mechanical energy that can be converted into thermal energy

is 100%.

You have an empty 20 oz. soda bottle and you blow air over the opening to excite a fundamental standing wave. Now, you slice off the bottom of the bottle (it's plastic) without changing its length very much. You blow over the opening and excite a fundamental standing wave in the bottle with its bottom end open. The frequency of the standing wave in the second case

is higher than that in the first case.

A string is clamped at both ends and then plucked so that it vibrates in a standing mode between two extreme positions a and c. Let upward motion correspond to positive velocities. When the string is in position b, the instantaneous velocity of points along the string -string with three labeled points a, b, and c

is zero, positive, or negative, depending on the position along the string.

A hand moves to produce a periodic wave. You are making a movie. You freeze the movie and get this snapshot. If you advance the movie one frame, the know at point A would be -image of hand scribbling line

lower.

The volume of a gaseous sample is increased from V1 to V2 in three different ways. A-->B: isobaric process A-->C: isothermal process A-->D: adiabatic process Then the work done by the gas is (graph with a line for each)

maximum in the isobaric process

In simple harmonic motion

none of the above.

A hypothetical engine operates in a cycle taking in 10,000 J from a hot reservoir and 5000 J from a cold reservoir. In the cycle, it forms 15,000 J of work. Such an engine

obeys the first law of thermodynamics but violates the second law of thermodynamics.

Assume we can change the equilibrium state of a system via two different processes. Assume that the initial and the final state are the same. Which of the quantities ΔU, ΔQ, ΔW, and ΔT must be the same for the two processes?

only ΔU and ΔT

Two objects in thermal equilibrium have the same

temperature.

The maintenance of the life cycle depends on

the presence of a source and a sink of energy.

Suppose you have an aquarium. You have a solid plastic decoration and a rock of about the same volume but the rock has twice the mass. Both are totally submerged in the water. The buoyant force on the plastic object is about -picture of fish tank

the same as that on the rock.

A sinusoidal force with a given amplitude is applied to an oscillator. To maintain the largest amplitude oscillation, the frequency of the applied force should be

the same as the natural frequency of the oscillator.

You are watching a semi truck bounce up and down on a spring. (Yep it's a toy.) At the topmost point in the truck's path,

the truck's velocity is zero but its acceleration is downward.

The liquid level in a glass thermometer rises as the temperature increases because

the volume expansion coefficient of glass is less than that of the liquid.

A sine wave and a square wave cannot have the same

tone quality.

Sound does not pass through

vacuum.

While a guitar string is vibrating, you gently touch the midpoint of the string to ensure that the string does not vibrate at that point. The lowest-frequency standing wave that could be present on the string

vibrates at twice the fundamental frequency.

In a popular classroom demonstration, a cotton ball is placed in the bottom of a strong test tube. A plunger fits inside the tube and it makes an air-tight seal. It is then pushed down very rapidly, and the cotton flashes and burns. This happens because

when the air gets compressed its temperature increases.