Waves and Sound Practice Test 43 points total Free- response part: [27 points]

Transcription

1 Name Waves and Sound Practice Test 43 points total Free- response part: [27 points] 1. To demonstrate standing waves, one end of a string is attached to a tuning fork with frequency 120 Hz. The other end of the string passes over a pulley and is connected to a suspended mass M as shown in the figure. The value of M is such that the standing wave pattern has four "loops." The length of the string from the tuning fork to the point where the string touches the top of the pulley is 1.20 m. The linear density of the string is 1.0 x 10 4 kg/m, and remains constant throughout the experiment. a. Determine the wavelength of the standing wave. [2 pts] b. Determine the speed of transverse waves along the string. [3 pts] c. If a point on the string at an antinode moves a total vertical distance of 4 cm during one complete cycle, what is the amplitude of the standing wave? [2 pts] d. Calculate the value of M, the mass hanging from the end of the string. (3 pts) e. The speed of waves along the string increases with increasing tension in the string. Indicate whether the value of M should be increased or decreased in order to double the number of loops in the standing wave pattern. Justify your answer. [4pts]

2 2. You are performing the resonance lab like the one we did in class, only this time with a much longer tube. The tuning fork has a frequency of 440 Hz. The first resonance is heard at 0.18 m from the top of the tube. The temperature in the room is 21 C. a) The water level is lowered until the next resonance is heard. What is the length of the air column for this resonance? [6 pts] b) The water level is lowered AGAIN until a third resonance is heard. What is the length of the air column for this third resonance? [2 pts] 3. An open organ pipe has a length of 55 cm. The temperature of the air in the pipe is 22 C. Calculate the frequency of the first 3 harmonics that can be played on this organ pipe. [5 pts]

3 Multiple Choice Part: [16 points] 1. A small vibrating object S moves across the surface of a ripple tank producing the wave fronts shown above. The wave fronts move with speed v. The object is traveling in what direction and with what speed relative to the speed of the wave fronts produced? Direction Speed (A) To the right Equal to v (B) To the right Less than v (C) To the right Greater than v (D) To the left Less than v (E) To the left Greater than v 2. A cord of fixed length and uniform density, when held between two fixed points under tension T, vibrates with a fundamental frequency f. If the tension is doubled, the fundamental frequency is (A) 2f (B) (C) f ( D) (E) 3. A vibrating tuning fork sends sound waves into the air surrounding it. During the time in which the tuning fork makes one complete vibration, the emitted wave travels (A) one wavelength (B) about 340 meters (C) a distance directly proportional to the frequency of the vibration (D) a distance directly proportional to the square root of the air density (E) a distance inversely proportional to the square root of the pressure 4.. Two wave pulses. each of wavelength i., are traveling toward each other along a rope as shown above. When both pulses are in the region between points X and Y, which are a distance λ. Apart, the shape of the rope will be which of the following?

4 5. Two sinusoidal functions of time are combined to obtain the result shown in the figure above. Which of the following can best be explained by using this figure? (A) Beats (B) Doppler effect (C) Resonance (D) Standing Waves Questions 6-7 A standing wave of frequency 5 hertz is set up on a string 2 meters long with nodes at both ends and in the center, as shown above. 6. The speed at which waves propagate on the string is (A) 0.4 m/s (B) 2.5 m/s (C) 5 m/s (D) 10 m/s (E) 20 m/s 7. The fundamental frequency of vibration of the string is (A) 1 Hz (B) 2.5 Hz (C) 5 Hz (D) 7.5 Hz (E) 10 Hz 8. In the Doppler effect for sound waves, factors that affect the frequency that the observer hears include which of the following? I. The speed of the source II. The speed of the observer III. The loudness of the sound (A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III 9. Waves in which the particles of the medium oscillate perpendicular to the velocity of the wave are called. (a) longitudinal (b) sound (c) transverse (d) reflected 10. The fundamental frequency heard on an organ pipe (open at both ends) is 40 Hz. What are the next three harmonics which can be produced on this organ pipe? (a) 120 Hz, 200 Hz, 280 Hz (b) 80 Hz, 160 Hz, 320 Hz (c) 80 Hz, 120 Hz, 160 Hz 11. The nth overtone on an organ pipe is 300 Hz. The (n+1)th overtone (the next higher one) is 450 Hz. Is this an open- closed pipe or an open- open pipe? (a) open- closed (b) open- open (c) cannot tell without more information.

5 12. In the diagram above, a stationary source located at point S produces sound having a constant frequency of 512 hertz. Observer A, 50. meters to the left of S, hears a frequency of 512 hertz. Observer B, 100. meters to the right of S, hears a frequency lower than 512 hertz. Which statement best describes the motion of the observers? (a) Observer A is moving toward point S, and observer B is stationary. (b) Observer Ais moving away from point S, and observer B is stationary. (c) Observer A is stationary, and observer B is moving toward point S. (d) Observer A is stationary, and observer B is moving away from point S. 13. What is the wavelength of a kilohertz sound wave traveling at 326 meters per second through air? (a) m (b) 7.67 m (c) 1.30 m (d) 130. m 14.The graph above represents the displacement of a particle in a medium over a period of time. The amplitude of the wave is (a) 4.0 s (b) 8 cm (c) 2.0 s (d) 4 cm Questions A longitudinal wave moves to the right through a uniform medium, as shown below. Points A, B, C, D, and E represent the positions of particles of the medium. 15. Which diagram best represents the motion of the particle at position C as the wave moves to the right? (a) 1 (b) 2 (c) 3 (d) The wavelength of this wave is equal to the distance between points (a) A and B (b) B and C (c) A and C (d) B and E