Exam 4

Question 1

Three identical springs each have the same spring constant k. If these three springs are attached end to end forming a spring three times the length of one of the original springs, what will be the spring constant of the combination?

k/3
1.73k
k
3k

Answer 1

k/3

Question 2

Two springs, each with spring constant k, are attached end to end in a series fashion. A second pair of identical springs are also attached in series fashion. Then the pair of series attached springs are attached in parallel to each other. What is the effective spring constant of the resulting combination of springs?

k/2
2k
k
either k/4 or 4k

Answer 2

k

**k_eff1 + k_eff2 = k/2 + k/2 = k

Question 3

Which one of the following quantities is at a maximum when an object in simple harmonic motion is at its maximum displacement?

kinetic energy
frequency
speed
acceleration

Answer 3

acceleration

**due to equation ma=-kx

Question 4

Which one of the following quantities is at a maximum when an object in simple harmonic motion is at its maximum displacement?

kinetic energy
frequency
speed
acceleration

Answer 4

acceleration

**due to equation ma=-kx

Question 5

For a mass suspended on a spring in the vertical direction, the time for one complete oscillation will depend on:

the maximum speed of the oscillating mass.
the value for g (the acceleration due to gravity).
the distance the mass was originally pulled down.
the time doesn’t depend on any of the above.

Answer 5

the time does not depend on any of these

**time to complete one oscillation can be d=vt

Question 6

The kinetic energy of the bob on a simple pendulum swinging in simple harmonic motion has its maximum value when the displacement from equilibrium is at what point in its swing?

1/2 the amplitude
1/4 the amplitude
zero displacement
equal the amplitude

Answer 6

zero displacement

*** energy is fastest closest to the equilibrium position

Question 7

When car shock absorbers wear out and lose their damping ability, what is the resulting oscillating behavior?

critically damped
hyperdamped
overdamped
underdamped

Answer 7

underdamped

***friction reduces total energy of the system and the oscillations is said to be damped
LOSE damping = underdamped

Question 8

For a wave on the ocean, the amplitude is:

the height difference between a crest and a trough.
the distance between crests.
one half the height difference between a crest and a trough.
how far the wave goes up on the beach.

Answer 8

one half the height difference between a crest and a trough

Question 9

As a gust of wind blows across a field of grain, a wave can be seen to move across the field as the tops of the plants sway back and forth. This wave is a:

interference of waves.
longitudinal wave.
transverse wave.
polarized wave.

Answer 9

longitudinal wave

**areas of high and low pressure are longitudinal waves

Question 10

If the frequency of a traveling wave train is increased by a factor of three in a medium where the speed is constant, which of the following is the result?

wavelength is one third as big
amplitude is one third as big
amplitude is tripled
wavelength is tripled

Answer 10

wavelength is 1/3 as big

**v=f*wavelength

Question 11

Which of the following is an example of a longitudinal wave?

sound wave in air and wave traveling in a string
wave traveling in a string
sound wave in air
neither sound wave in air nor wave traveling in a string

Answer 11

sound wave in air

Question 12

The wavelength of a traveling wave can be calculated if one knows the:

frequency.
frequency and speed.
amplitude and frequency.
speed and amplitude.

Answer 12

frequency and speed

Question 13

The superposition principle has to do with which of the following?

the ability of some waves to move very far
relativistic wave behavior
how displacements of interacting waves add together
effects of waves at great distances

Answer 13

how displacements of interacting waves add together

Question 14

If a wave pulse is reflected from a free boundary, which of the following choices best describes what happens to the reflected pulse?

doubled in amplitude
becomes inverted
halved in amplitude
remains upright

Answer 14

remains upright

Question 15

A mass-spring system on a horizontal frictionless surface is set in simple harmonic motion with amplitude A. The mass is then doubled and the system is again set into simple harmonic motion with the same amplitude. Which of the following is true about the total mechanical energy of the system due to doubling the mass?

It has halved.
It has quadrupled.
It has doubled.
It has not changed.

Answer 15

it has not changed

• *Total mechanical energy of system=1/2KA^2
• mass is not involved

Question 16

If a long spring with spring constant k is cut into 4 equal lengths, what is the spring constant of each of the 4 shorter springs?

It is 4 k.
It is still k.
It is k/16.
It is k/4.

Answer 16

it is 4k

**By logic and using the Ideal spring Equation F = -kx, where F is the force applied, k is the spring constant and x is the compressed distance.

Lets take a 9 coil spring and apply a force, the spring compresses say 0.9 cm, so each coil compresses 0.1 cm, by the same logic if the spring where cut to 3, the same force would compress this spring by 0.3cm. So using the equation, we can deduce that spring constant will be three times if the spring is cut into three.

Question 17

When an object is moving in simple harmonic motion, which of the following is at a minimum when the displacement from equilibrium is zero?

the total mechanical energy
the kinetic energy
the magnitude of the acceleration
the magnitude of the velocity

Answer 17

the magnitude of acceleration

**in simple harmonic oscillations, the acceleration is directly proportional to the displacement and opposite to its direction. So when the displacement of an object is at zero, y=0, and acceleration is at minimum.
a=-w^2y

Question 18

A pendulum on the Earth has a period T. The acceleration of due to gravity on Mars is less than that on the Earth, and the acceleration due to gravity on the Moon is even less. Where would the period of an identical pendulum be the least?

on the Moon
on Mars
on the Earth
The period of a pendulum would be the same on the Earth, Moon, and Mars since the period depends on the pendulum’s length which is the same for identical pendula.

Answer 18

on Earth

**equation: T=2pi*sqroot(L/g)
the larger g is, the smaller T will be

Question 19

Suppose there is an object for which F = +kx. What will happen if the object is moved away from equilibrium (x = 0) and released?

It will move further away with increasing acceleration.
It will return to the equilibrium position.
It will move further away with constant acceleration.
It will move further away with constant velocity.

Answer 19

it will move further away with increasing acceleration

**negative sign indicates that the force is always
directed opposite to the displacement, so if it is positive, it will move away from the equilibrium

Question 20

When a sine wave is used to represent a sound wave, the crest corresponds to:

condensation.
point where molecules vibrate at a right angle to the direction of wave travel.
region of low elasticity.
rarefaction.

Answer 20

condensation

Question 21

The speed of sound in air is a function of which one of the following?

frequency
temperature
wavelength
amplitude

Answer 21

temperature

** temperature at which speed of sound is varies
0C- 343
20C- 331

Question 22

Comparing the speed of sound in liquids, gases, and solids, the speed of sound is usually lowest in \_\_\_\_ and highest in \_\_\_\_. 
 liquids, solids 
 gases, liquids 
 solids, liquids 
 gases, solids

Answer 22

gases, solids

**speed of sound thru steel: 5700m/s
speed of sound thru air: 343

Question 23

If the intensity of a sound is increased by a factor of 100, how is the decibel level changed? The new decibel level will be:

double the old one.
two units greater.
ten times greater.
twenty units greater.

Answer 23

twenty units greater

**increasing by factor of 10 adds 10 to the dB level, increasing by factor of 100 adds 20 to the dB level

Question 24

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

faster and faster.
some constant speed faster than the normal speed of sound in air.
equal to the normal speed of sound in air.
slower than the normal speed of sound in air.

Answer 24

equal to the normal speed of sound in air

**because the velocity of the sound in a medium does not change with the motion of the source .
even though the frequency is changed , the change will be compensated by the change in the wave length keeping the velocity constant
v= λ f

Question 25

Consider a vibrating string that makes a sound wave that moves through the air. As the guitar string moves up and down, the air molecules that are a certain horizontal distance from the string will move: up and down. in circles around the guitar string. toward and away from the guitar string. back and forth along the direction of the length of the string.

Answer 25

toward and away from the guitar string **if a vibrating spring generates sound waves then air molecules move toward and away from the string. This generates the string to move up and down

Question 26

``` When I stand halfway between two speakers, with one on my left and one on my right, a musical note from the speakers gives me constructive interference. How far to my left should I move to obtain destructive interference? one wavelength half a wavelength one and a half wavelengths one-fourth of a wavelength ```

Answer 26

one fourth of a wavelength

Question 27

When a sound wave moves through a medium such as air, the motion of the molecules of the medium is in what direction (with respect to the motion of the sound wave)? anti-parallel (in opposite direction) perpendicular parallel parallel and anti-parallel (in opposite direction)

Answer 27

parallel and antiparallel

Question 28

For a standing wave on a string the wavelength must equal: twice the distance between adjacent nodes. the distance between adjacent antinodes. the distance between adjacent nodes. the distance between supports.

Answer 28

twice the distance between adjacent nodes **The Distance between the two adjacent nodes = Wavelength/2 So Wavelength = 2 * The Distance between the two adjacent nodes

Question 29

Which of the following ranges corresponds to the longest wavelengths? infrasonic ultrasonic audible all have the same wavelengths

Answer 29

infrasonic **ultrasonic has a higher frequency, so its wavelength is lower, infrasonic has a lower frequency so it will have a longer wavelength

Question 30

When the standing wave pattern in a pipe is NANA, the pipe has which of the following set of properties? (N stands for node, A for antinode.) It is open at both ends. It is open at one end and closed at the other end. It is closed at both ends. Any of the above could be true.

Answer 30

It is open at one end and closed at the other end. **If one end of the air column is closed, a node must exist at this end since the movement of the air is restricted If the end is open, the elements of the air have complete freedom of movement and an antinode exists

Question 31

``` For a standing wave in an air column in a pipe that is open at both ends, there must be at least: two nodes and one antinode. two nodes and two antinodes. one node and one antinode. two antinodes and one node. ```

Answer 31

two antinodes and one node. **open open- ANA closed open- closed end (N), open end (A)

Question 32

``` The air in a tube open at both ends is sent into its fundamental resonance. One end of the tube is then closed and the air column is again set into its fundamental resonance. The resonant frequency ____ after the end is closed. stays the same halves increases by a factor of 1.4 doubles ```

Answer 32

halves **denominator in equation for a open open tube is 2L, while the denominator for an open closed tube is 4L. Therefore the speed will be slower with a large denominator

Question 33

``` What phenomenon is created by two tuning forks, side by side, emitting frequencies, which differ by only a small amount? interference resonance beats the Doppler effect ```

Answer 33

beats **Beats are alternations in loudness, due to interference Waves have slightly different frequencies and the time between constructive and destructive interference alternates

Question 34

``` The number of overtones, and their relative intensities, is associated with what property of the tone generated by a musical instrument? quality interference pattern range attack pattern ```

Answer 34

quality

Question 35

If the air temperature decreases, how does the resonant frequency in a pipe closed at one end change? It doesn't change because resonance is pressure phenomenon. It increases. It doesn't change since one end of the pipe is closed. It decreases.

Answer 35

it decreases ** if the velocity of sound (v) changes, the frequency will also change. Higher temperature = faster velocity = higher frequency lower temperature = slower velocity = lower frequency

Question 36

The air in a pipe resonates at 150 Hz and 750 Hz, one of these resonances being the fundamental. If the pipe is open at both ends, how many resonances are between the two given ones, and if the pipe is closed at one end, how many resonances are between the two given ones? open: 0; closed: 2 open: 2; closed: 0 open: 3; closed: 1 open: 1; closed: 3

Answer 36

**open resonates at 150, 300, 450,600,750 | closed resonates at 150,450,750

Question 37

``` An airplane flying with a constant speed flies from a warm air mass into a cold air mass. The Mach number will: decrease. become unstable. increase. stay the same. ```

Answer 37

increases **The speed of sound is proportionate to sqrt (Temperature), hence when the airplane flies to colder region, the local speed of sound decreases, which implies the mach number defined to be speed of plane / local speed of sound increases

Question 38

A relatively new medical device that uses ultrasonics is referred to by the acronym CUSA. What does the letter A stand for? array audible aspirator accumulator

Answer 38

aspirator