 # Third Hour Exam

## November 3, 1998

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E) none of the above

Possibly useful information:

v = x / t p = m v T = 2  a = v / t PE = m g h T = 2  v = vi + a t PE = (1/2) k x2 v = x = xi + vi t + (1/2) a t2 KE = (1/2) m v2 v=(wavelength) x (frequency)

v = r  F = k x L = (n) x (half wavelength)

F = m a Ei = Ef

F12 = - F21 pi = pf

w = mg F = p / t

g = 9.8 m/s2 10 m/s2

For every question, also consider as a possible answer

E) none of the above

1. Increasing the amplitude of a simple pendulum makes its period

A) longer

B) shorter

C) unchanged

2. Increasing the mass of a simple pendulum makes its period

A) longer

B) shorter

C) unchanged

3. Increasing the length of a simple pendulum makes its period

A) longer

B) shorter

C) unchanged

4. Increasing the amplitude of a mass-and-spring simple harmonic oscillator makes its period

A) longer

B) shorter

C) unchanged

5. Increasing the mass of a mass-and-spring simple harmonic oscillator makes its period

A) longer

B) shorter

C) unchanged

6. A mass-and-spring simple harmonic oscillator has maximum kinetic energy

A) at its equilibrium position

B) when its displacement equals its amplitude

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

7. A mass-and spring simple harmonic oscillator has maximum potential energy at

A) at its equilibrium position

B) when its displacement equals its amplitude

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

8. The amplitude of a simple harmonic oscillator is

A) the time required for one oscillation

B) the number of oscillators per second

C) the energy stored in the oscillations

D) the maximum distance moved from equilibrium

9. The period of a simple pendulum depends upon its

A) mass

B) amplitude

C) length

D) all of the above

10. The period of a certain simple harmonic oscillator is 0.1 s; its frequency is

A) 0.1 Hz

B) 1.0 Hz

C) 10.0 Hz; f = 1/T, f = 1/(0.1 s) = 10/s = 10 cyc/s = 10 Hz

D) 100 Hz

11. Ordinary household electricity is alternating current with a frequency of 60 Hz. Its period is

A) 60 cycles per second

B) 120 cycles per second

C) 0.0167 s; T = 1/f = 1/(60 Hz) = 1/(60 cyc/s) = (1/60) s = 0.0167 s

D) 0.0333 s

12. If you apply a force to an oscillator at its natural frequency, you will produce motion

A) at exactly twice that frequency

B) at exactly one-half that frequency

C) with large amplitude

D) with an amplitude that dies out or gets smaller.

13. There are "signals" of many different frequencies coming into the antenna of your radio. Only the one with a particular frequency is amplified and produces the sound you listen to. This is an example of

A) damping

B) amplitude degeneration

C) timbre or quality

D) resonance

14. If a carefully calibrated pendulum were over a very large oil deposit, where the acceleration due to gravity is slightly decreased, what would happen to the pendulum's period?

A) increase; T = 2  B) stay the same

C) decrease

15. Where is the speed of a simple harmonic oscillator zero?

A) at its equilibrium position

B) when its displacement equals its amplitude

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

16. Like a transverse wave, a longitudinal wave has a/an

A) amplitude

B) frequency

C) wavelength

D) all of the above

17. Which of the following is a longitudinal wave?

A) light

B) wave on a string

C) sound

D) all of the above

18. The individual vibrations or disturbances of a transverse wave move

A) in the same direction as the wave itself

B) perpendicular to the wave itself

19. A wave has a frequency of 100 Hz and travels 25 m in one second. It has

A) a wave speed of 25 m/s and a wavelength of 4 m.

B) a wave speed of 25 m/s and a wavelength of 0.25 m.

v = (wavelength) x (frequency)

v = 25 m/s = (wavelength) x (100 Hz)

25 m/s = (wavelength) x (100 1/s)

wavelength = 0.25 m

C) a wave speed of 100 m/s and a wavelength of 25 m

D) a wave speed of 100 m and a wavelength of 4 m

20. For standing waves, nodes are

A) always a wavelength apart; nodes are half a wavelength apart

B) regions of greatest amplitude; nodes have minimum (zero!) amplitude

C) regions of greatest frequency; all parts of a standing wave have the same frequency

D) always two wavelengths apart ; nodes are half a wavelength apart

E) none of the above

21. For standing waves, antinodes

A) are half a wavelength apart

B) have the greatest amplitude

C) alternate with nodes

D) all of the above

22. For standing waves on a string,

A) a node is located at each end

B) a whole number times half the wavelength equals the length of the string

C) the whole "pattern" of standing waves occurs only for certain frequencies

D) all of the above

23. For standing waves on a string,

A) an antinode is located at each end

B) the length of the string equals the wavelength divided by a whole number

C) the amplitude is proportional to the frequency

D) all of the above

E) none of the above

24. On a string that is 1.0 m long, standing waves may be formed with the following wavelengths:

A) 1.0 m, 2.0 m, 3.0 m

B) 1.0 m, 2.0 m, 4.0 m

C) 3.0 m, 1.5 m, 0.75 m

D) 2.0 m, 1.0 m, 0.5 m 25. Standing waves can occur when

A) the frequency equals the wavelength

B) the amplitude exceeds the wavelength

C) a wave is reflected back on itself

D) a wave's period equals its wavelength

26. A node is

A) always in the middle of a standing wave

B) a position of maximum amplitude

C) a position of minimum amplitude

D) equal to the fundamental frequency

27. Light and sound are both waves. You can see a ringing bell inside an evacuated glass container but you can not hear it. This is because

A) of resonance

B) light travels faster than sound

C) sound requires air to be transmitted and light does not

D) light passes through glass but sound does not

28. A bobber on a fishing line oscillates up and down three times per second as waves pass by. The waves have a frequency of

A) (1/3) Hz

B) 3 Hz

C) (1/3) sec

D) 3 sec

29. A bobber on a fishing line oscillates up and down two times per second as waves pass by. The waves have a wavelength of 10 cm. The waves are traveling at

A) 5 cm/s

B) 10 cm/s

C) 20 cm/s

f = 2 Hz = 2 cyc/s

v = (wavelength) x (frequency)

v = (10 cm) x ( 2 / s)

v = 20 cm/s

D) 980 cm/s

30. If you put your fingertip in a pool of water and repeatedly move it up and down, you will create circular water waves that move out from that point. What will happen to the wavelength of these waves if you move your finger up and down more slowly (or less frequently)?

A) increase
v = (wavelength) x (frequency)

A decrease in frequency means an increase in wavelength.

B) remain the same

C) decrease

31. Sound is

A) an electromagnetic wave
light is an electromagnetic wave

radio and television and X-rays are also electromagnetic waves

B) a polarized wave

only transverse waves can be polarized

longitudinal waves can not be polarized

C) a transverse wave

D) a longitudinal wave

32. "Supersonic" means

A) lower than the range of human hearing

B) higher than the range of human hearing

C) faster than the speed of sound

D) slower than the speed of sound

33. "Ultrasonic" means

A) lower than the range of human hearing

B) higher than the range of human hearing

Our MacMotion detectors in the MBL use ultrasound.

Ultrasound is used for medical imaging.

Bats and dolphins use ultrasound for echolocation.

C) faster than the speed of sound

D) slower than the speed of sound

34. "Infrasonic" means

A) lower than the range of human hearing

B) higher than the range of human hearing

C) faster than the speed of sound

D) slower than the speed of sound

35. Bats and dolphins use echolocation to navigate or the find food or to find their way without relying on sight. The frequencies they use are

A) supersonic

B) infrasonic

C) ultrasonic

Both bats and dolphins use ultrasound with frequencies of about 50 kHz and above.

D) microsonic

36. If you double the frequency of a sound wave, you also double its

A) wavelength; doubling the frequency means you reduce the wavelength to one-half

B) speed; changing the frequency should have no effect on the speed.

C) amplitude ; changing the frequency should have no effect on the amplitude.

D) all of the above

E) none of the above

37. The range of human hearing is about

A) 10 Hz to 100 Hz

B) 50 Hz to 500 Hz

C) 50 Hz to 20 000 Hz

This means alarms should go off -- flags go up and alarms sound -- if you find that a note on a keyboard has a frequency of 0.220 Hz or 0.440 Hz or 0.880 Hz. That is _really_ infrasonic!!!!!

D) 1 000 Hz to 100 000 Hz

38. Sound travels fastest in

A) air (a gas)

B) water (a liquid)

C) steel (a solid)

The inter-molecular forces that hold a molecule in place in a solid are much stronger than those in a liquid or a gas so they move the molecule more rapidly -- just like a mass attached to a stronger spring. This more rapid movement of the molecules means that sound is transmitted faster too.

D) vacuum

39. The speed of sound in air depends upon

A) wavelength

B) frequency

C) temperature

D) amplitude

40. Increasing the length of a vibrating string will

A) decrease its resonance frequency
Increasing the length of the string means the wavelength of the standing wave is also increased. And increase in wavelength means a decrease in the frequency.

B) decrease its amplitude

C) increase its amplitude

D) increase its resonance frequency

41. Ella Fitzgerald made commercials for Memorex in which she used her voice to break a wine glass. This is an example of

A) echolocation

B) reflected sound

C) ultrasonic frequencies

D) resonance

42. Beats are heard when two sounds have

A) nearly the same amplitude

B) nearly the same frequencies

C) twice the amplitude

D) exactly twice the wavelength

43. The fundamental frequency present in a sound is the

A) sum of all the frequencies mixed together

B) difference between the highest and lowest frequencies present

C) lowest frequency present

D) highest frequency present

44. The "pitch" of a sound is determined by its

A) overtones frequencies

B) harmonics frequencies

C) fundamental frequency

D) resonance frequencies

45. The quality or timbre -- the distincitive characteristic -- of a sound is determined by its

A) overtones or harmonics

B) amplitude or loudness

C) attack or decay

D) fundamental frequency

46. You hear beats with a frequency of 3 Hz when you strike a tuning fork that vibrates at 256 Hz and a chime. The chime has a frequency of

A) 3 x 256 Hz = 768 Hz

B) 259 Hz

fbeat = difference in frequencies = f2 - f1 = 3 Hz

3 Hz = f2 - 256 Hz

f2 = 259 Hz

C) (256 / 3) Hz = 85.3 Hz

D) 250 Hz

47. The fundamental frequency of a violin string is 440 hertz. The frequency of its second harmonic is

A) 110 Hz

B) 220 Hz

C) 440 Hz

D) 880 Hz

48. Consider a musical note of 440 hertz ("concert 'A'"). Two octaves higher is represented by a musical note of

A) 220 Hz; this is one octave lower.

B) 880 Hz ; this is one octave higher.

C) 1320 Hz

D) 1760 Hz

One octave above A at 440 Hz is twice that frequency, 880 Hz.

One octave above that A at 880 Hz is 1760 Hz.

49. The intensity or loudness of a musical sound is related to the sound wave's

A) wavelength

B) frequency

C) amplitude

D) wave speed

50. Suppose you play a note of a certain pitch on a violin. You can produce a lower-pitched note by

A) shortening the length of the string that is allowed to vibrate

B) increasing the tension of the string

C) decreasing the linear mass density of the string

D) lengthening the part of the string that vibrates.

The other three choices will each RAISE the pitch of the note.

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