 Excursions in Physics
Third Hour Exam
October 26, 2001

Statistics:

High: 92

Mean 71

Low : 50  For every question, also consider as a possible answer
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 F = – k x v = r F = – k x fb = | f1 - f2 | F = m a Ei = Ef v = (freq) x (wavelength) F12 = - F21 pi = pf L = [n] x [wavelength/2] 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 frequency
A) longer
B) shorter
C) unchanged; The period of any simple harmonic oscillator is independent of the amplitude. This makes simple harmonic oscillators very useful in time keeping devices -- like watches.

2. Increasing the mass of a simple pendulum makes its frequency
A) longer
B) shorter
C) unchanged

3. Increasing the length of a simple pendulum makes its frequency
A) longer; the period becomes longer.
B) shorter; f = 1/T; the frequency becomes smaller
C) unchanged

4. Increasing the amplitude of a mass-and-spring simple harmonic oscillator makes its period
A) longer
B) shorter
C) unchanged; The period of any simple harmonic oscillator is independent of the amplitude. This makes simple harmonic oscillators very useful in time keeping devices -- like watches.

5. Increasing the mass of a mass-and-spring simple harmonic oscillator makes its period
A) longer; With more mass, it is more difficult to move the mass or it moves more s-l-o-w-l-y.
B) shorter
C) unchanged

6. A mass-and-spring simple harmonic oscillator has maximum kinetic energy
A) at its equilibrium position; At its equilibrium position, the potential energy is a minimum (or zero) so the kinetic energy must be a maximum.
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. The loudness of a sound is associated with its
A) frequency.
B) wavelength.
C) velocity.
D) amplitude.

8. The period 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 frequency of a mass-and-spring simple harmonic oscillator is independent of its
A) mass.
B) spring constant.
C) amplitude. The period or frequency of any simple harmonic oscillator is independent of the amplitude. This makes simple harmonic oscillators very useful in time keeping devices -- like watches.
D) all of the above.

10. The period of a certain simple harmonic oscillator is 0.2 s; its frequency is
A) 0.5 Hz
B) 5.0 Hz; f = 1/T = 1/(0.2 s) = 5 (1/s) = 5 (cyc/s) = 5 Hz
C) 50.0 Hz
D) 500 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) s = 0.0167 s
D) 0.0583 s

12. If you apply a force to an oscillator at its natural frequency, you will produce motion with
A) exactly twice that frequency
B) exactly one-half that frequency
C) large amplitude
D) an amplitude that damps 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 iron ore deposit, where the acceleration due to gravity is slightly increased, what would happen to the pendulum's period?

A) increase
B) stay the same
C) decrease; With a larger pull due to gravity, the force pulling it back to equilibrium will be more so it will respond more quickly, giving a shorter period.

[[ I checked the key and it was, indeed, marked "C". ]]

15. Where is the speed of a simple harmonic oscillator zero?
A) at its equilibrium position
B) when (or where!) 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) 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 longitudinal wave move
A) in the same direction as the wave itself
B) perpendicular to the wave itself

19. A wave has a frequency of 50 Hz and travels 25 m in one second. It has
A) a wave speed of 25 m/s and a wavelength of 0.5 m; v = (freq)x(wavelength); 25 m/s = (50/s) x (0.5 m) = 25 m/s
B) a wave speed of 25 m/s and a wavelength of 2.0 m
C) a wave speed of 200 m/s and a wavelength of 2.0 m
D) a wave speed of 200 m and a wavelength of 0.5 m

[[ I checked the key and it is, indeed, marked "A". ]]

20. For standing waves, nodes are
A) always a wavelength apart; nodes are always half a wavelength apart
B) regions of greatest amplitude; nodes have minimum amplitude (zero if everything works right!)
C) regions of greatest frequency; everything about a standing wave has the same frequency.
D) always two wavelengths apart; nodes are always 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, such as a guitar 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, such as a guitar string,
A) an antinode is located at each end; The ends are fixed and an antinode has maximum amplitude!
B) the length of the string equals the wavelength divided by a whole number; A whole number times half the wavelength equals the length of the string.
C) the amplitude is proportional to the frequency; no.
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:
(hint: draw a diagram!)
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; zero amplitude if everything's working right!
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; v = (freq)x(wavelength) = (2/s)x(10 cm) = 20 cm/s
D) 200 cm/s

30. The lowest frequency present in a sound determines its
A) pitch.
B) amplitude.
C) beat frequency.
D) quality or timbre.

31. Sound that we might describe as “noise” has
A) a large amplitude.
B) no period.
C) a high frequency.
D) a short wavelength.

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; ultra sound is used in medical imaging and is used by bats and dolphins in echolocation.
C) faster than the speed of sound
D) slower than the speed of sound

34. The harmonics present in a sound determine its
A) pitch.
B) amplitude.
C) beat frequency.
D) quality or timbre.

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
D) microsonic

36. When two waves interfere and cause a larger amplitude, this is known as
A) echolocation.
B) destructive interference.
C) constructive interference.
D) resonance.

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 kHz
D) 1 kHz to 100 kHz

38. Ultrasound can be used to make images of the insides of a body. Ultrasound has the advantage of providing high resolution due to its
A) small wavelength. Remember, v = (freq) x (wavelength) so a HIGH (or LARGE) frequency corresponds to a small wavelength.
B) very long wavelength.
C) small amplitude.
D) low frequency.

39. A “sonic boom” occurs
A) only at the moment an aircraft “breaks” the sound barrier.
B) when the cone of high pressure following behind a supersonic airplane encounters people or buildings.

C) when there is a temperature inversion.
D) only over water.

40. Increasing the length of a vibrating string will
A) decrease its resonance frequency
B) decrease its amplitude
C) increase its amplitude
D) increase its resonance frequency

41. Bats and dolphins emit high-pitched sound and use its reflection to find food and to navigate without sight. This is known as
A) echolocation
B) absorbed sound
C) infrasonic frequencies
D) resonance

42. Unlike billiard balls, waves can pass through each other. This is known as
A) echolocation.
B) resonance.
C) superposition.
D) interactive collisions.

43. When a boat goes faster than the speed of surface waves on a lake it produces
A) breakers that have a frequency that is twice that of the boat’s.
B) breakers that have a frequency the same as the boat’s.
C) “white caps” with “froth” at the top of the waves.
D) a large bow wave.

44. The "pitch" of a sound is determined by its
A) overtones frequencies
B) harmonics frequencies
C) fundamental frequency; this fundamental frequency is the lowest frequency present.
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) 253 Hz; fbeat = f1 - f2; the beat frequency is the difference of the two frequencies that are heard together. If we hear a beat frequency of 3 Hz and know one of the frequencies is 256 Hz the other frequency must be either 253 Hz or 259 Hz.
C) 250 Hz
D) (256 / 3) Hz = 85.3 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

49. If you listen to the horn on a railroad engine as it approaches you and then recedes from you, you will notice a change in the pitch. You will hear
A) the approaching train sound lower and then go higher as it leaves.
B) the approaching train sound louder and then become softer as it leaves.
C) the approaching train sound higher and then go lower as it leaves.
D) the approaching train sound softer and then become louder as it leaves.

50. If you listen to the horn on a railroad engine as it approaches you and then recedes from you, you will notice a change in the pitch. This is described as the
A) Newton’s sound effect.
B) Doppler effect.  