Question

The pattern of sound waves emitted by a source traveling at constant velocity is shown in the figure below. Each of the wave fronts shown in the image was emitted when the source was at one of the blue dots shown in the image. (a) In what direction is the source moving? to the right Oto the left (b) What is the ratio of the speed of the source to the speed of sound? 2 (c) If you are at rest at point A, and the source is emitting waves that have a frequency of 120 Hz, what frequency do you observe? 119

Answer 1

Given that The pattern of sound waves emitted by a source travelling at constant velocity is shown in fig a) The Source is moving to the left since the wire fronts are more spaced out to the right (receding direction) b) In a time + Seconds, the distance roved by a waive emitted by the right - most source = 5 units In time, the distance covered by the source is d = 2 units so, ratio of speed source to speed of sound is: V/C = 5/2 = 2.5 In time t, the distance covered by the wave front = 5 units. so 5 = c t In time it's the distance covered by the wave front from the point to its left = 4 units 4 = c t� also t� - t = d/v = 2/v 2/v = [5 - 4]/c Therefore v/c = 2 c) observed frequency at A will be: f = f_0 v/c - 1/v/c + 1 = + 60 Hz