Q71 of 118 Page 352

Figure (16-E11) shows a person standing somewhere in between two identical tuning forks, each vibrating at


512 Hz. If both the tuning forks move towards right at a speed of 5.5 m s-1, find the number of beats heard by the listener. Speed of sound in air = 330 m s-1.


Let us assume that the fork in the left side is fork A and the other one is fork B.


Now, A they are moving, the fork A is reaching the person and the fork B is going away from the person. Hence, the frequencies will be,



And,



So, the beat frequency will be,





Here,


f0 = 512 Hz


v = 330 ms-1


vs =5.5 ms-1


Putting the values, we get,




More from this chapter

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69

A violin player riding on a slow train plays a 440 Hz note. Another violin player standing near the track plays the same flute, When the two are close by and the train approaches the person on the ground, he hears 4.0 beats per second. The speed of sound in air = 340 m/s. (a; Calculate the speed of the train. (b) What beat frequency is heard by the player in the train?

 70

Two identical tuning forks vibrating at the same frequency 256 Hz are kept fixed at some distance apart. A listener runs between the forks at a speed of 3.0 m/s so that he approaches one tuning fork and recedes from the other (figure 16-E10). Find the beat frequency observed by the listener. Speed of sound in air = 332 m/s.


 72

A small source of sound vibrating at frequency 500 Hz is rotated in a circle of radius 100/π cm at a constant angular speed of 5.0 revolutions per second. A listener situates himself in the plane of the circle. Find the minimum and the maximum frequency of the sound observed. Speed of sound in air = 332 m s-1.

 73

Two trains are travelling towards each other both at a speed of 90 km h-1. If one of the trains sounds a whistle at 500 Hz, what will be the apparent frequency heard in the other train? Speed of sound in air = 350 m s-1.