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# As the drawing illustrates, a siren can be made by blowing a jet of air through 20 equally spaced holes in a rotating disk. The time it takes for successive holes to move past the air jet is the period of the sound. The siren is to produce a 2200-Hz tone. What must be the angular speed $\omega(\text { in rad/s) of the }$ disk?

## angular velocity $=691.15 \mathrm{rad} / \mathrm{s}$

#### Topics

Sound and Hearing

Wave Optics

### Discussion

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##### Andy C.

University of Michigan - Ann Arbor

LB
##### Marshall S.

University of Washington

### Video Transcript

in this problem on the topic off waves and sound, we're told that a siren can be made by blowing Egypt of a through 20 equally spaced holes in irritating disk. Yeah, we take the time that it takes for success of holes to move past the edge it as the period of sound and were given the frequency off the stone. We want to calculate the angular speed Omega off this disc. Now we know that the will must rotate at a frequency F, which is 2000 200 hearts divided by the number off holes, which is 20. So the frequency off the rotations must be 100 and 10 hunts. And so the angular speed omega we know is defined as two pi times different Quincy F. Yeah. So this is two pi times 100 and tin huts, which gives us the angular frequency off. 690 radiance. The second. Yeah,

University of Kwazulu-Natal

#### Topics

Sound and Hearing

Wave Optics

##### Andy C.

University of Michigan - Ann Arbor

LB
##### Marshall S.

University of Washington