Physics II- Exam 1

You have a long pipe and a short pipe. Which one has the higher frequency?

. the short pipe - the standing wave within a shorter pipe must have a shorter wavelength but the same wave speed (in the air). This requires a higher frequency.

The range of frequencies the typical young human can hear is:

20 Hz to 20,000 Hz

A boat is moored in a fixed location and waves make it move up and down. If the spacing between wave crests is 40 M and the speed of the waves is 5 M/s, how long does it take the boat to go from top of the crest to the bottom of a trough?

4 second - The wavelength is 40 M (crest to crest) so the crest to trough is half a wavelength, 20 M. The speed is 5M in one second so it take 4 seconds to move from the crest to the trough.

A mass on a spring exhibits SHM and has amplitude, A and period, T. What is the total distance covered by the mass during a time interval of T?

4A - the mass will travel from equilibrium out to the amplitude (1A) back to equilibrium (1A) from equilibrium to the amplitude on the other side (1A) and then back to equilibrium (1A)

A particular string resonates in four loops at a frequency of 280 Hz. Name at least three other frequencies at which it will also resonate

70 Hz, 140 Hz, 210 Hz

Open Tube

Antipodes exist at both ends because the air is free to move. Standing wave requires a minimum of one node within the tube to exist. Corresponds to the fundamental frequency of the tube

Nodes

Are points of destructive interference

Displacement

As a wave propagates through a medium the individual particles are displaced from equilibrium and this disturbance that is organized as a wave is called the displacement

Velocity of the wave

At turning point partial has 0 velocity. The velocity of a particle on the string is maximum at 0 displacement.

Mechanical Waves

Can only travel within a material medium Ex. Air and water, sound waves, waves along a string are mechanical

Two kinds of interference

Destructive Interference Constructive Interference

A wave transports both matter and energy.

False

A wave transports matter but not energy

False

A wave transports neither matter nor energy, it just moves itself from one place to another.

False

Closed Tube

Forced to have a node at the closed end and an antipodes at the open end. Only 1/4 of the wavelength compromises the fundamental harmonic, only odd harmonics are possible with this configuration. Ex. Organ pipe

Hookes Law

Fsp=-kx

Amplitude

Greatest distance the mass moves from the equilibrium point

The Doppler Effect

If a source is moving toward or away from an observer, the observer hears a frequency that is shifted from that of the source

Wave transport Energy

In a vice through a cord the particles of the cord are moved upward (or downward) from their equilibrium position and gain kinetic and potential energy via that displacement

A pendulum clock is known to be accurate at sea level. It is then moved to a location at high altitude. In this new location the clock will

Lose time (seem to run to slow) - the equation for the period of a pendulum includes gravity in the denominator.

Range of Human Hearing

Most sensitive between 2000 Hz and 4000 Hz

Frequency

Number of cycles completed in one second

Sinusoidal Waves

Periodic in both space and time. The frequency of the wave is the frequency of the oscillation of the source. Waves do not transport material, they transport energy

Antinodes

Points of constructive interference.

Sound

Requires a medium to travel through and is longitudinal wave

A guitar string vibrates at a frequency of 330 Hz with wavelength 1.4 m. The frequency and wavelength of this sound in air at 20oC as it reaches our ears is:

Same frequency, shorter wavelength

The Doppler Shift

Shift in frequency can be calculates if we consider how the apparent wavelength changes as the source moves

The medium

Substance through or along which waves move. The medium MUST be elastic which means it requires a restoring force. The medium itself DOES NOT flow with the wave

The string below is fixed at both ends and has a standing wave as shown. The arrows are pointing at a part of the standing wave called...?

The Nodes - The nodes are points of perfect destructive interference

You are driving at 85 km/h. Your sister follows you in the car behind at 85 km/h. When you honk your horn, your sister hears a frequency:

The Same frequency you hear

The Law of Reflection

The angle of reflection equals the angle of incidence.

The string below is fixed at both ends and has a standing wave as shown. The arrows are pointing at a part of the standing wave called...? (The crest of the wave)

The antinodes

Transverse wave

The displacement of a transverse wave is perpendicular to the direction of travel. Ex. Electromagnetic waves, wave in a cord

Longitudinal Wave

The displacement of particles in the medium for a longitudinal wave move parallel to the direction of travel Ex. Sound waves

Resonant Frequencies

The frequency where standing waves occur

An ambulance is approaching your position as you stand waiting at a cross walk. The frequency of the ambulance's siren is about 2500 Hz and it is moving at 15 m/s. Which is the following statements is true in this situation?

The frequency you hear is higher than 2500 Hz

An ambulance has just sped past your position as you stand waiting at a cross walk. The frequency of the ambulance's siren is about 2500 Hz and it is moving away from you at 15 m/s. Which is the following statements is true in this situation?

The frequency you hear is lower than 2500 Hz

Standing Waves

The result of a wave interference when a string is fixed at one end is vibrated with the proper frequency. Reflected waves interfere with the generated wave to produce a standing wave in the string.

The picture shows a standing wave on a string that is fixed at both ends. This standing wave represents which harmonic?

The second Harmonic - if there are two antipodes it must be the second harmonic

Period

The time required to complete one cycle shown by variable T

You decide to go hiking in the mountains on a hot summer day and you discover a small canyon where you can easily cause an echo. You time the echoes, and it takes 2 seconds for them to reach your ears. Winter time arrives and you choose a very cold day to hike back to the same canyon. You listen to your echoes in the cold air and discover:

The winter time echo is slower to reach you than the summer time echo. It takes a bit more than 2 seconds to reach you. - Sound moves faster in hotter temperatures

Loudness is related to the amount of energy per unit time crossing a unit area

True

The frequency of a simple periodic wave is always equal to the frequency of its source.

True

Sounds with frequencies that exceed 20,000 Hz are called:

Ultrasonic

Beats

Variations in the intensity of sound generated by two different but similar frequency source caused by interference of sound waves Beat frequency is equal to the difference between the frequencies of the two waves

When a sound wave passes from air to water do you expect the frequency or the wavelength to change?

Wavelength

Principle of Superposition

When waves overlap the algebraic cum of their individual displacements becomes the displacement of the medium at that point

Is the acceleration of a SHO ever zero?

Yes. At the equilibrium position

You drop a rock into a well, and you hear the splash 2.5 s later. If the depth of the well were doubled, how long after you drop the rock would you hear the splash in this case?

between 2.5 seconds and 5 seconds later - Gravity causes the rock to fall faster for the increased distance, but the speed of sound is the same. This means it will be greater, but not double the time.

When a sound wave passes from air into water, what properties of the wave will change?

both the speed of the wave and the wavelength - The frequency does not change, but the speed does. If that is true, then the wavelength must also change.

Sound waves are a particular type of wave, they are:

longitudinal waves

A mass on a spring is performing SHM and has amplitude A and period T. At what point in the motion is v = 0 and a = 0 simultaneously?

none of these answers is correct. -The only place that acceleration is zero is when it passes through equilibrium. velocity can not be zero at that location while the mass is performing SHM

Two pendula have the same mass, m, but different string lengths, L. How do their periods, T, compare to each other?

the period, T, is larger for the longer length string - the period of a pendulum is proportional to the square root of L/g so the larger L results in a longer period.

A mass oscillates in SHM with amplitude A. If the mass is doubled, but the amplitude is not changed, what will happen to the total energy of the system?

the total energy will not change - the energy in a SHM system is proportional to the squared amplitude... not the mass.

A mass on a spring is performing SHM and has amplitude A and period T. At what point in the motion is v = vmax and a = 0 simultaneously?

x=0