Q86 of 118 Page 352

A source emitting sound at frequency 4000 Hz, is moving along the Y-axis with a speed of 22 m s-1, A listener is situated on the ground at the position (660 m, 0). Find the frequency of the sound received by the listener at the instant the source crosses the origin. Speed of sound in air = 330 m s-1.

Let us assume when the source is at A it produces the sound that reaches P when the source comes to the origin. If vs is the source velocity and v is the velocity of sound then,




And



Now we can find the cosine of the angle made.




The frequency will be,






More from this chapter

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84

An operator sitting in his base camp sends a sound signal of frequency 400 Hz. The signal is reflected back from a car moving towards him. The frequency of the reflected sound is found to be 410 Hz. Find the speed of the car. Speed of sound in air = 324 m s-1.

 85

Figure (16-E12) shows a source of sound moving along the X-axis at a speed of 22 m s continuously emitting a sound of frequency 2-0 kHz which travels in air at a speed of 330 m s-1. A listener Q stands on the Y-axis at a distance of 330 m from the origin. At t = 0, the source crosses the origin P. (a) When does the sound emitted from the source at P reach the listener Q? (b) What will be the frequency heard by the listener at this instant? (c) Where will the source be at this instant?


 87

A source of sound emitting a 1200 Hz note travels along a straight line at a speed of 170 m s-1. A detector is placed at a distance of 200 m from the line of motion of the source. (a) Find the frequency of sound received by the detector at the instant when the source gets closest to it. (b) Find the distance between the source and the detector at the instant it detects the frequency 1200 Hz. Velocity of sound in air = 340 m s-1.

 88

A small source of sound S of frequency 500 Hz is attached to the end of a light string and is whirled in a vertical circle of radius 16 m. The string just remains tight when the source is at the highest point. (a) An observer is located in the same vertical plane at a large distance and at the same height as the center of the circle (figure 16-E13). The speed of sound in air = 330 m s-1 and g = 10 m s-2. Find the maximum frequency heard by the observer. (b) An observer is situated at a large distance vertically above the center of the circle. Find the frequencies heard by the observer corresponding to the sound emitted by the source when it is at the same height as the center.