Conceptual Questions

ssm Solution is in the Student Solutions Manual

| 1 | Considering the nature of a water wave (see Figure 16-4), describe the motion of a fishing float on the surface of a lake when a wave passes beneath the float. Is it really correct to say that the float bobs straight up and down? Explain.

| 2 | “Domino Toppling” is one entry in the Guinness Book of World Records. The event consists of lining up an incredible number of dominoes and then letting them topple, one after another. Is the disturbance that propagates along the line of dominoes transverse, longitudinal, or partly both? Explain.

| 3 | Suppose that a longitudinal wave moves along a Slinky at a speed of 5 m/s. Does one coil of the Slinky move through a distance of 5 m in one second? Justify your answer.

| 4 | ssm Examine Conceptual Example 3 before addressing this question. A wave moves on a string with a constant velocity. Does this mean that the particles of the string always have zero acceleration? Justify your answer.

| 5 | A wire is strung tightly between two immovable posts. Discuss how an increase in temperature affects the speed of a transverse wave on this wire. Give your reasoning, ignoring any change in the mass per unit length of the wire.

| 6 | A rope of mass m is hanging down from the ceiling. Nothing is attached to the loose end of the rope. A transverse wave is traveling on the rope. As the wave travels up the rope, does the speed of the wave increase, decrease, or remain the same? Give a reason for your choice.

| 7 | One end of each of two identical strings is attached to a wall. Each string is being pulled tight by someone at the other end. A transverse pulse is sent traveling along one of the strings. A bit later an identical pulse is sent traveling along the other string. What, if anything, can be done to make the second pulse catch up with and pass the first pulse? Account for your answer.

| 8 | In Section 4.10 the concept of a “massless” rope is discussed. Would it take any time for a transverse wave to travel the length of a massless rope? Justify your answer.

| 9 | In a traveling sound wave, are there any particles that are always at rest as the wave passes by? Justify your answer.

| 10 | Do you expect an echo to return to you more quickly or less quickly on a hot day than on a cold day, other things being equal? Account for your answer.

| 11 | ssm A loudspeaker produces a sound wave. Does the wave length of the sound increase, decrease, or remain the same, when the wave travels from air into water? Justify your answer. (Hint: The frequency does not change as the sound enters the water.)

| 12 | Jell-O starts out as a liquid and then sets to a gel. What would you expect to happen to the speed of sound in this material as the Jell-O sets? Does it increase, decrease, or remain the same? Give your reasoning.

| 13 | Some animals rely on an acute sense of hearing for survival, and the visible part of the ear on such animals is often relatively large. Explain how this anatomical feature helps to increase the sensitivity of the animal’s hearing for low-intensity sounds.

| 14 | A source is emitting sound uniformly in all directions. There are no reflections anywhere. A flat surface faces the source. Is the sound intensity the same at all points on the surface? Give your reasoning.

| 15 | If two people talk simultaneously and each creates an intensity level of 65 dB at a certain point, does the total intensity level at this point equal 130 dB? Account for your answer.

| 16 | Two cars, one behind the other, are traveling in the same direction at the same speed. Does either driver hear the other’s horn at a frequency that is different from that heard when both cars are at rest? Justify your answer.

| 17 | A source of sound produces the same frequency underwater as it does in air. This source has the same velocity in air as it does underwater. The observer of the sound is stationary, both in air and underwater. Is the Doppler effect greater in air or underwater when the source (a) approaches and (b) moves away from the observer? Explain.

| 18 | A music fan at a swimming pool is listening to a radio on a diving platform. The radio is playing a constant-frequency tone when this fellow, clutching his radio, jumps off. Describe the Doppler effect heard by (a) a person left behind on the platform and (b) a person down below floating on a rubber raft. In each case, specify (1) whether the observed frequency is greater or smaller than the frequency produced by the radio, (2) whether the observed frequency is constant, and (3) how the observed frequency changes during the fall, if it does change. Give your reasoning.

| 19 | ssm When a car is at rest, its horn emits a frequency of 600 Hz. A person standing in the middle of the street hears the horn with a frequency of 580 Hz. Should the person jump out of the way? Account for your answer.

| 20 | The text discusses how the Doppler effect arises when (1) the observer is stationary and the source moves and (2) the observer moves and the source is stationary. A car is speeding toward a large wall and sounds its horn. Is the Doppler effect present in the echo that the driver hears? If it is present, from which of the above situations does it arise, (1) or (2) or both? Explain.

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