# 14 Modern Physics Questions

See attached file for full problem description.

1. A certain string on a piano is tuned to produce middle C

(f = 261.63 Hz) by carefully adjusting the tension is the string. For a

fixed wavelength, what is the frequency when this tension is

doubled?

a. 130.08 Hz

b. 185.00 Hz

c. 370.00 Hz

d. 446.63 Hz

e. 523.26 Hz

2. A bell is ringing inside of a sealed glass jar that is connected to a

vacuum pump. Initially, the jar is filled with air. What does one

hear as the air is slowly removed from the jar by the pump?

a. The sound intensity gradually decreases

b. The frequency of the sound gradually increases

c. The frequency of the sound gradually decreases

d. The speed of the sound gradually increase

e. The sound intensity of the bell does not change

3. The Young's modulus of aluminum (density = 2700 kg/m3) is

6.9 × 1010 N/m2. Determine the speed of sound in an aluminum rod.

a. 1.4 × 103 m/s

b. 2.5 × 103 m/s

c. 5.1 × 103 m/s

d. 6.3 × 103 m/s

e. 7.0 × 103 m/s

4. Two boys are whispering in the library. The radiated sound power

from one boy's mouth is 1.2 × 10-9 W and it spreads out uniformly in

all directions. What is the minimum distance the boys must be

away from the librarian so that she will not be able to hear them?

The threshold of hearing for the librarian is 1.00 × 10-12 W/m2/

a. 100 m

b. 35 m

c. 23 m

d. 16 m

e. 9.8 m

5. At a distance of 5.0 from a point sound source, the sound intensity

level is 110 dB. At what distance is the intensity level 95 dB?

a. 5.0 m

b. 7.1 m

c. 14 m

d. 28 m

e. 42 m

6. The car in the figure is moving to the left at 35 m/s. The car's horn

continuously emits a 2.20 × 102 Hz sound. The figure also shows

the first two regions of compression of the emitted sound waves.

The speed of sound is 343 m/s. How far does the car move in one

period of the sound emitted from the horn?

a. 0.08 m

b. 0.16 m

c. 8 m

d. 16 m

e. 35 m

7. Two pulses of identical shape travel toward each other in opposite

directions on a string, as shown in the figure. Which one of the

following statements concerning the situation is true?

a. The pulses will reflect from each other

b. The pulses will diffract from each other

c. The pulses will interfere to produce a standing wave

d. The pulses will pass through each other and produce beats

e. As the pulses pass through each other, they will interfere

destructively.

8. Sound waves are emitted from two speakers. Which one of the

following statements about sound wave interference is false?

a. In a region where both destructive and constructive

interference occur, energy is not conserved

b. Destructive interference occurs when two waves are exactly

out of phase when they meet

c. Interference redistributes the energy carried by the

individual waves.

d. Constructive interference occurs when two waves are exactly

in phase when they meet

e. Sound waves undergo diffraction as they exit each speaker

9. Two loudspeakers are located 3 m apart on the stage of an

auditorium. A listener at point P is seated 29.0 m from one speaker

and 25.0 from the other. A signal generator drives the speakers in

phase with the same amplitude and frequency. The wave amplitude

at P due to each speaker alone is A. The frequency is then varied

between 20 Hz and 300 Hz. The speed of sound is 343 m/s.

At what frequency or frequencies will the listener at P hear a

maximum intensity?

a. 170 Hz only

b. 113 Hz and 226 Hz

c. 86 Hz, 170 Hz, 257 Hz

d. 57 Hz, 113 Hz, 170 Hz, 227 Hz, and 284 Hz

e. 43 Hz, 85 Hz, 128 Hz, 170 Hz, 213 Hz, 257 Hz, and 298 Hz

10. For a diffraction horn loudspeaker, the sound emerges through a

rectangular opening. The opening of a diffraction horn has a width

of 0.15 m. If the speaker emits a continuous tome with a

wavelength of 0.11 m, at what angle does the first minimum occur?

a. 47°

b. 39°

c. 23°

d. 12°

e. 8.4°

11. A guitar string produces 4 beats/s when sounded with a 250 Hz

tuning fork and 9 beats per second when sounded with a 255 Hz

tuning fork. What is the vibrational frequency of the string?

a. 240 Hz

b. 246 Hz

c. 254 Hz

d. 259 Hz

e. 263 Hz

12. One string on a guitar is exactly in tune. The guitarist uses this

string to produce a tone with a frequency of 196 Hz by pressing

down at the proper fret. An adjacent string can also be used to

produce this tone without being pressed against a fret. However,

this adjacent string is out of tune and produces a tone that sounds

lower in frequency than the other tone. When the tones are

produced simultaneously, the beat frequency is 5.0 Hz. What

frequency does the adjacent string produce?

a. 196 Hz

b. 191 Hz

c. 171 Hz

d. 201 Hz

e. 186 Hz

13. A cylindrical tube sustains standing waves at the following

frequencies: 600 Hz, 800 Hz, and 1000 Hz. The tube does not

sustain standing waves at 500 Hz, at 900 Hz, at any frequencies

between 600 and 800 Hz, or at any frequencies between 800 and

1000 Hz. Determine the fundamental frequency of the tube and

whether the tube is open at both ends or has only one end open.

a. 50 Hz, both ends

b. 100 Hz, one end

c. 100 Hz, both ends

d. 200 Hz, one end

e. 200 Hz, both ends

×

μμμ

×

×

×

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μ

14 . What is the electric flux passing through a Gaussian surface that

surrounds a +0.075 C point charge?

a. 8.5 × 109 N?m2/C

b. 6.8 × 108 N?m2/C

c. 1.3 × 107 N?m2/C

d. 4.9 × 106 N?m2/C

e. 7.2 × 105 N?m2/C

https://brainmass.com/physics/flux-flux-density/14-modern-physics-questions-104489

#### Solution Preview

Here are the explanations of the answers:

1c = 261.63 * sqrt(2)

2a : the speed, and therefore the frequency, are determined by the ...

#### Solution Summary

Very brief explanation is given in addition to the answers.

Modern Physics Multiple Choice Questions

1. Use the work-energy theorem to find the force required to accelerate

an electron (m = 9.11 x 10-31 kg) from rest to a speed of 1.50 x 107 m/s

in a distance of 0.0125 m.

a. 8.20 x 10-15 N

b. 5.47 x 10-22 N

c. 8.20 x 10-17 N

d. 1.64 x 10-14 N

e. 3.56 x 10-19 N

2. Use the work-energy theorem to find the force required to accelerate

an electron (m = 9.11 x 10-31 kg) from rest to a speed of 1.50 x 107 m/s

in a distance of 0.0125 m.

a. 8.20 x 10-15 N

b. 5.47 x 10-22 N

c. 8.20 x 10-17 N

d. 1.64 x 10-14 N

e. 3.56 x 10-19 N

3. A ceiling fan has five blades, each with a mass of 0.34 kg and length of

0.66 m. The fan is operating in its "low" setting at which the angular

speed is 9.4 rad/s. If the blades can be approximated as uniform thin

rods that rotate about one end, what is the total rotational kinetic

energy of the five blades?

a. 35 J

b. 29 J

c. 23 J

d. 17 J

e. 11 J

4. The spring constant for the spring in a special cannon is 1800 N/m. In

cocking the cannon, the spring is compressed 0.55m. What is the initial

speed of a 7.0-kg cannonball at rest on the free end of the spring when

it is released?

a. 77 m/s

b. 140 m/s

c. 12 m/s

d. 8.8 m/s

e. 16 m/s

5. A cylinder with a radius of 0.120 m is placed between the plates of a

hydraulic press as illustrated in the drawing. A 4.45 x 105 -N force is

applied to the cylinder. What is the pressure on the end of the cylinder

due to the applied force?

a. 9.84 x 106 Pa

b. 3.13 x 105 Pa

c. 6.18 x 106 Pa

d. 5.34 x 104 Pa

e. 3.71 x 106 Pa

6. A child wants to pump up a bicycle tire so that its pressure is 2.5 x 105

Pa above that of atmospheric pressure. If the child uses a pump with a

circular piston 0.035 m in diameter, what force must the child exert?

a. 120 N

b. 240 N

c. 340 N

d. 930 N

e. 1300 N

7. The two dams are identical with the exception that the water reservoir

behind dam A extends twice the horizontal distance behind it as that of

dam B. Which one of the following statements regarding these dams is

correct?

a. The force exerted by the water on dam A is greater than that on

dam B.

b. The force exerted by the water on dam B is greater than that on

dam A.

c. Dam A is more likely to collapse than dam B if the water level

rises.

d. Dam B is more likely to collapse than dam A if the water level

rises.

e. The horizontal distance of the water behind the two dams does

not determine the force on them.

8. The density of ice is 0.92 g/cm3, and the density of seawater is 1.03

g/cm3. A large iceberg floats in Artic waters. What fraction of the

volume of the iceberg is exposed?

a. 0.080%

b. 11%

c. 89%

d. 92%

e. 99%

9. Alyssa went to her outside faucet to fill a 0.032-m3 bucket with water

to wash her car. Water exits with a speed of 0.64 m/s. The radius of the

faucet is 0.0075 m. How long does it take to fill the bucket completely?

a. 9.0 s

b. 17 s

c. 190 s

d. 280 s

e. 890 s

10. The coefficient of linear expansion of a certain solid is 9 x 10-6/C°.

Assuming this solid behaves like most solids, what is its coefficient of

volume expansion?

a. 9.1 x 10-6/C°

b. 27 x 10-36/C°

c. 27 x 10-6/C°

d. 729 x 10-6/C°

e. 729 x 10-36/C°

11. A 2.00-kg metal object requires 5.02 x 103 J of heat to raise its

temperature from 20.0°C to 40.0°C. What is the specific heat capacity

of the metal?

a. 63.0 J/(kg?C°)

b. 126 J/(kg?C°)

c. 251 J/(kg?C°)

d. 502 J/(kg?C°)

e. 1.00 x 103 J/(kg?C°)

12. A 0.20-kg lead shot is heated to 90°C and dropped into an ideal

calorimeter containing 0.50 kg of water initially at 20.0°C. What is the

final equilibrium temperance of the lead shot? The specific heat

capacity of lead is 128 J/(kg?C°), and the specific heat of water is 4186

J/(kg?C°).

a. 4.8°C

b. 20.8°C

c. 22.4°C

d. 27.8°C

e. 42.1°C

13 . Heat is added to a sample of water in an insulated container. Which

one of the following statements is necessarily true?

a. The temperature of the water will rise.

b. The volume of the water must decrease.

c. The mass of the system must decrease.

d. Under certain conditions, the temperature of the water can

decrease.

e. The type of change that will occur depends on the original

temperature of the water.