5 An electric fan in room at 25 °C is producing a small sound in a swinging mode from its frame. The source of sound is assumed to be coming with the interaction of flow and the guarding frame wire. The emitted sound frequency is assumed to be independent of the swinging angle. Maximum instantaneous swinging angular velocity is assumed to be 1 rad/s, and sound velocity in stationary air at 25 °C is 344 m/s. In case of 3 m/s of emitted wind speed and of 300 Hz of emitted fluid dynamic frequency, the detected sound frequency by a person just in front of the fan is (1) (a) exactly constant with time, (b) strongly varying ( more than 1 % ). (c) weakly varying ( less than 1 %). The highest or constant detected frequency by the person is (2) (a) more than 307 Hz, (b) approximately 306 Hz, (c) approximately 303 Hz, (d) approximately 300 Hz, (e) approximately 297 Hz. The detected frequency by a person standing far away is (3) (a) nearly constant with time, (b) strongly varying (more than 1 % ), (c) weakly varving (le than 1%
5 An electric fan in room at 25 °C is producing a small sound in a swinging mode from its frame. The source of sound is assumed to be coming with the interaction of flow and the guarding frame wire. The emitted sound frequency is assumed to be independent of the swinging angle. Maximum instantaneous swinging angular velocity is assumed to be 1 rad/s, and sound velocity in stationary air at 25 °C is 344 m/s. In case of 3 m/s of emitted wind speed and of 300 Hz of emitted fluid dynamic frequency, the detected sound frequency by a person just in front of the fan is (1) (a) exactly constant with time, (b) strongly varying ( more than 1 % ). (c) weakly varying ( less than 1 %). The highest or constant detected frequency by the person is (2) (a) more than 307 Hz, (b) approximately 306 Hz, (c) approximately 303 Hz, (d) approximately 300 Hz, (e) approximately 297 Hz. The detected frequency by a person standing far away is (3) (a) nearly constant with time, (b) strongly varying (more than 1 % ), (c) weakly varving (le than 1%
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Transcribed Image Text:5 An electric fan in room at 25 °C is producing a small sound in a swinging mode
from its frame. The source of sound is assumed to be coming with the interaction
of flow and the guarding frame wire. The emitted sound frequency is assumed to
be independent of the swinging angle. Maximum instantaneous swinging angular
velocity is assumed to be 1 rad/s, and sound velocity in stationary air at 25 °C is
344 m/s.
In case of 3 m/s of emitted wind speed and of 300 Hz of emitted fluid dynamic
frequency, the detected sound frequency by a person just in front of the fan is
(1) (a) exactly constant with time,
(b) strongly varying ( more than 1 % ).
(c) weakly varying ( less than 1 % ).
The highest or constant detected frequency by the person is
(2) (a) more than 307 Hz,
(b) approximately 306 Hz.
(c) approximately 303 Hz,
(d) approximately 300 Hz,
(e) approximately 297 Hz.
The detected frequency by a person standing far away is
(3) (a) nearly constant with time,
(b) strongly varying (more than 1 % ),
(c) weakly varying ( less than 1 % ).
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