Physics 234 Spring 2001 Exam 1 Friday, February 23, 2001

Version **A**: 1D, 2A, 3B, 4B, 5C, 6B, 7A, 8A, 9C, 10B, 11A, 12E,
13E, 14A, 15C, 16A, 17B, 18A, 19E, 20B

Version **B** had the same questions but the answers were swapped:

1B, 2C, 3D, 4E, 5B, 6D, 7D, 8E, 9C, 10D, 11E, 12E, 13C, 14D, 15C, 16C, 17D, 18E, 19A, 20D

1. A particle is in simple harmonic motion with period T. At time t = 0 it is at the lowest point. At which of the following times is it at the highest point point?

A) 1.4T B) 0.25T C) T D) 0.5T E) 1.5T

2. An object attached to one end of a spring makes 20 vibrations in 10s. The frequency of oscillation is:

A) 2 Hz B) 10 Hz C) 0.5 Hz D) 5 Hz E) 0.20 Hz

3. It is impossible for two particles, each executing simple harmonic motion, to remain in phase with each other if they have different:

A) masses B) periods C) amplitudes D) spring constants E) kinetic energies

4. A restoring force that tends to bring pendulum back to its central position (and is responsible for oscillations) is:

A) 2.m.g.sinQ B) m.g.sinQ C) m.g.sinQ/Ö 2 D) m.g.cosQ E) m.g.tanQ

5. A mass-spring system is oscillating with amplitude A. The kinetic energy will equal the potential energy only when the displacement is

A) zero B) ±A/4 C) ±A/Ö 2 D) ±A/2 E) anywhere between -A and +A

6. A wave is described by y(x,t) = 15.cos(60^{0}).sin(5x - 20t+p/2), where x and y are in centimeters and t
is in seconds. The amplitude is:

A) 5.0 cm B) 7.5 cm C) 15.0 cm D) 20.0 cm E) 30.0 cm

7. A wave is described by y(x,t) = 15.cos(60^{0}).sin[p.(5x - 20t + ^{1}/_{2})],
where x is in meters, y is in centimeters and t is in seconds. The frequency of wave is:

A) 10 Hz B) 5 Hz C) 20 Hz D) 20/5 Hz E) 7.5 Hz

8. A wave is described by y(x,t) = 15.cos(60^{0}).sin[p.(5x - 20t)], where x is in meters, y is in
centimeters and t is in seconds. The smallest distance (along the x axis) between the two
points of 45^{0} phase difference is:

A) 0.05 m B) 0.10 m C) 0.20 m D) 0.40 m E) 0.80 m

9. The displacement of a string carrying a traveling sinusoidal wave is given by y(x,t)
= y_{m}sin(kx-wt-f)

At time t = 0 the point at x = 0 has a displacement of ( -y_{m} ) and is moving
in the positive y direction. The phase constant f is:

A) 0 B) p/4 C) p/2 D) p E) ^{3p} /_{4
}

10. A standing wave on a string is given by y(x,t) = 0.25.sin[p (5x+1/2)].cos(4t).

The distance between the two adjacent nodes is:

A) 0.1 m B) 0.2 m C) 0.4 m D) 0.8 m E) 1.40 m

11. A fire whistle emits a tone of 680 Hz. Take the speed of sound in air to be 340 m/s. The wavelength of this sound is about:

A) 0.5 m B) 1.0 m C) 2.0 m D) 3.0 m E) 3.40 m

12. During a time interval of exactly one period of vibration of a tuning fork, the emitted sound travels a distance (speed of sound in air is about 330 m):

A) equal to the length of the tuning fork B) equal to twice the length of the tuning fork C) of about 330 m D) which decreases with time

E) of one wavelength in air

13. A person is talking in a small room; and the sound intensity level is 60 dB everywhere within the room. If there are eight people talking simultaneously in the room, what is the sound intensity level?

A) 60 dB B) 79 dB C) 74 dB D) 64 dB E) 69 dB

14. The intensity of a certain sound wave is 6 microwatts/cm^{2}. If its
intensity is raised by 10 decibels, the new intensity (in microwatts/cm^{2}) is:

A) 60 B) 6.6 C) 6.06 D) 600 E) 12

15. Two pipes are each open at one end and closed at the other. Pipe A has length L and pipe B has length 3L. Which harmonic of pipe B matches in frequency the fundamental of pipe A?

A) The fundamental B) The second C) The third D) The fourth E) There are none

16. Five organ pipes are described below. Which one has the highest frequency fundamental?

A) an 8 ft open pipe B) a 10 ft open pipe C) a 5 ft closed pipe D) a 9 ft closed pipe E) a pipe in which the displacement nodes are 16 ft apart

17. Two small identical speakers are connected (in phase) to the same source. The speakers are 3 m apart and at ear level. An observer stands at X, 4 m in front of one speaker as shown. The sound he hears will be least intense if the wavelength is:

A) 1 m B) 2 m C) 3 m D) 4 m E) 5 m

18. In each of the following two situations a source emits sound with a frequency of 1000 Hz. In situation I the source is moving at 100 m/s toward an observer at rest. In situation II the observer is moving at 100 m/s toward the source, which is stationary. The speed of sound is 340 m/s. The frequencies heard by the observers in the two situations are:

A) I: 1417 Hz; II: 1294 Hz B) I: 1417 Hz; II: 1417 Hz C) I: 1294 Hz; II: 1294 Hz D) I: 773 Hz; II: 706 Hz E) I: 773 Hz; II: 773 Hz

19. A transverse periodic wave on a string with a linear density of 0.200 kg/m is described by the following equation:

y = 0.005 sin(419t - 21.0x), where x and y are in meters and t is in seconds. What is the tension in the string?

A) 3.99 N B) 32.5 N C) 42.1 N D) 65.8 N E) 79.6 N

20. A particle moves counterclockwise in a circle of radius 15 cm, making
1 revolution every 3s (w = 2p/3). At time t=0 the particle is on positive y axis (see fig). The
equation for x component of the position of the particle as a function of time is: A) x(t)=15.sin(wt+p/2) B) x(t)=15.cos(wt+p/2) C) x(t)=15.sin(wt) D) x(t)=15.cos(wt) E) x(t)=15.cos(-wt) |