test+fybnvc08+ch11 12+waves sound

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FyBNVC08 Ch11-12 Mechanical waves – Sound NV-College

In the multi-choice problems below just circle the correct answer (s) in the test paper.

1. If a violin string vibrates at Hz262 as its fundamental frequency, what are the

frequencies of first five harmonics? [1/0]

a. Hz , Hz , Hz f 2621 = f 5242 = f 7863 = , Hz f 04814 = , Hz f 31015 =

b. Hz , Hz , Hz f 2621 = f 7863 = f 31015 = , Hz f 83417 = , Hz f 35829 =

c. Hz , Hz , Hz f 2621 = f 5243 = f 7865 = , Hz f 04817 = , Hz f 31019 =

d. Hz , Hz , Hz f 2621 = f 7862 = f 31013 = , Hz f 83414 = , Hz f 35825 =

e. None above, they are:

Answer: Alternative ______

Why? Show a sample of your calculations. [1/0]

2. An organ pipe is cm7.32 long. What are the fundamental frequency and first four

overtones of the pipe at C °20 if it is closed at one end? At C °20 , the speed of sound in

air is sm /343 . [1/0]

a. Hz , Hz , Hz f 2621 = f 5242 = f 7863 = , Hz f 04814 = , Hz f 31015 =

b. Hz , Hz , Hz f 2621 = f 7863 = f 31015 = , Hz f 83417 = , Hz f 35829 =

c. Hz , Hz , Hz f 5241 = f 57413 = f 62225 = , Hz f 67137 = , Hz f 72049 =

d. Hz , Hz , Hz f 5241 = f 04912 = f 57413 = , Hz f 09824 = , Hz f 62225 =




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3. If the air temperature in a room is increased, the fundamental frequency of the organ

pipes

a) will not be effected.

b) will be decreased.

c) will be increased.

d) will be equal to the frequency of the second harmonics.



4. What resonant frequency would you expect from blowing an empty soda bottle that is

cm0. deep? What would the resonant frequency be if it was two-third filled? [1/0]18

a. Hz476 , and Hz715 respectively.

b. Hz476 , and Hz4301 respectively.

c. Hz953 , and Hz4301 respectively.

d. Hz953 , and Hz8582 respectively.



Why? Show your calculations in the space below. [1/1]





5. The velocity of waves on a string is sm /0. . If the frequency of the standing waves

is Hz475 , how far apart are two adjacent nodes? [2/0]

92

a. m968. 0

b. m68.9

c. cm68. ,9

d. m194. 0

e. None above its ___________


6. The mass of a harmonic oscillator of period s0.1 is tripled, i.e. 12 3mm = . The period

of the new harmonic oscillator is [2/0]

a) s31

b) s3

c) s3 .

d) s3

1

e) s9

Answer: Alternative : _______________





7. In an earthquake, it is noted that a footbridge oscillates at fundamental frequency of

period s5.2 . What other possible resonant periods of motion are there for this bridge?

[1/0]

a)

...,3,2 ,15.2=⋅

nsn

b) ...,3,2,15.2

1=

⋅ns

n

c) ...,3,2,12

5=ns

n

d) ...,3,2,15

2=ns

n.

e) None above. It is _________________

Answer: Alternative: _______________

Why? Show the detail of your calculations in the space provided below: [0/1]

8. Of the following procedures, which one (s) will higher the pitch of a guitar string? [1/0]

a) Decrease string tension.

b) Increase string tension.

c) Shorten the string.

d) Lengthen the string.

e) Use a heavier string.

f) Use a lighter string.

Answer: Alternative: _______________






9. Calculate the beat frequency if E above the middle C frequency at Hz330 and F above

the middle C frequency at Hz349 are played simultaneously. Will the beat be

audible? What if each played two octaves lower? Will the beat be audible? Note that a

frequency will be lowered by a factor of two if it is played at one octave lower.

a. The beat frequencies are Hz679 , audible, and Hz170 audible, respectively.

b. The beat frequencies are Hz679 , not audible, and Hz340 not audible,

respectively.

c. The beat frequencies are Hz19 , audible, and Hz75. audible, respectively.4

d. The beat frequencies are Hz19 , not audible, and Hz75. audible, respectively.4

e. The beat frequencies are Hz19 , audible, and Hz75. not audible, respectively.4

f. The beat frequencies are Hz19 , not audible, and Hz75. not audible,

respectively.

4

g. None above. They are:

Answer: Alternative: _________


10. The siren of a police car at rest emits a sound wave at Hz6001 . What frequency will

you hear, if you are at rest and the police car is approaching you at hkm /108 .a. I will hear the siren at Hz4711 .

b. I will hear the siren at Hz7531 .

c. I will hear the siren at Hz7401 .

d. I will hear the siren at Hz4601 .

e. I will hear the siren at Hz460 .2

f. I will hear the siren at Hz1851 .

g. None above. I will hear the siren at

Answer: Alternative: _________






11. Each figure below illustrates a transmitted wave, T , and a reflected wave, R .

Determine which medium is heavy (tätare) section and which medium is light (tunnare)

section. Note that the vertical dashed line just indicates the change of medium. Your

answer must include the direction of motion of the pulse, and the reason for your

conclusion in sufficient detail.

i. [1/1]Answer:

T R

sectionleft sectionright

ii. [1/1]Answer:

T R


iii. [1/1]

Answer:

T R


iv.

[1/1]Answer:

T R






12. The highest key on a piano corresponds to a frequency about 150 times that of the

lowest key.

a. If the string for the highest frequency is cm0.4 how long would the length of the

string corresponding to the lowest frequency have to be if it had identical linear

density and was under the same tension? Even for grand piano strings are not longer

than m3 . [1/1]

b. What should be done in order to reduce the length of the string corresponding to the

lowest frequency to m0.3 . Explain clearly your solution. [0/2]

13. Show that the amplitude A of circular water waves decreases as the square root of the

distance r from the sourcer

A1

∝ . Ignore damping. [0/2/¤]

14. A balsa wood block of mass gm Block 0.90= floats on a lake, bobbing up and down at a

frequency of Hz f Block 0.3=

a What is the value of the effective spring constant of water? [1/1]

b A partially filled water bottle of mass gmbottle 160= and almost the same size and

shape of the balsa block is tossed into the water. Calculate the period at which the

bottle may bob up and down? Assume simple harmonic oscillation. [1/1]

15. Niklas and Oscar designed an experiment to measure the velocity of sound in air. They

stayed at a considerable distance from a high building. The building was well isolated

and no other building is closed by. Niklas clapped and Oscar measured the time. Niklas

arranged the clapping time such that he clapped as he heard the echo of his previous clap

from the building. Oscar counted the number of Niklas’ clap. In average Niklas clapped

9 claps in s0.5 . Oscar measured the distance from the point Niklas clapped to the

building. It was m97 . Determine the value that Niklas and Oscar obtained for the

velocity of the sound in air. [0/2]

16. At a rock concert, a decibel-meter registered dB135 when placed m0.2 in front of a

loudspeaker on the stage.

a) Show that the power output of the speaker, assuming uniform spherical spreading of

the sound and neglecting absorption in the air is about kw6.1 . [0/2]

b) How far away would the intensity level be a somewhat reasonable dB90 ? [0/2]






17. An ambulance carrying a seriously injured patient moves down a h

velocity of hkm /126 . Its siren em ts a sound at

ighway at a constant

i Hz.400 .

Determine the frequency heard by a car driver moving in the

opposite direction at constant velocity of hkm /0.90

as the car approaches the ama. bulance. [0/2]

b. as the car moves away from the ambulance. [0/2]

18. Two pulses shown in the figure below are moving toward each other. Their speed are

identical.

a Sketch the shape of the string at the moment directly overlap. [0/2]

b Sketch the shape of the string a few moments later. [2/0]

-6

-4

-2

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

t [s]

y [ c m ]

a. Answer:

-6

-4

-2

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

t [s]

y [ c m ]

b. Answer:

-6

-4

-2

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

t [s]

y [ c m ]





19. ne end of a horizontal light string is attached to a small-amplitude vibrator. The string

e in sing. [0/2]

O

passes over a frictionless pulley a distance m L away, and a g100 is hung from the

other end. The figure below is printed in the scale 10:1 . The vibrator is connected to a

tone-generator as illustrated in the figure. You may assume the string at the generator isa node, which is nearly true. According to the manufacture of the string the mass of

m0.50 of the string is g75.1 .

a. Determine the speed of the wav

b. Calculate the frequency of the tone generator. [0/2/¤]

c. The length of the string may be adjusted by moving the pulley. If the hanging mass

is fixed at g100 , and the frequency of the vibrator is fixed at Hz500 , how many

different standing wave pattern may be achieved by varying L between cm10 and

cm150 ? [0/2/¤]

g100vibrator

oscillator tonefrequency

20. particular organ pipe can resonate atA Hz735 , Hz0291 , and Hz3231 , but not any

other frequencies between Hz735 and Hz3231 [0/6/¤]

a) Is this open or closed organ. Why? Show details of your calculation and explain

.

your reasoning. b) What is the fundament frequency of this pipe?

test+fybnvc08+ch11 12+waves sound

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