A whistle revolves in a circle with an angular speed of 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer, which is far away from the centre in the same plane ? $(v_{sound} = 340 m/s)$

(1) 333 Hz

(2) 374 Hz

(3) 385 Hz

(4) 394 Hz

A Siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s, frequency of the sound to be heard by the listener is (take velocity of sound as 330 m/s)

(1) 733.3 Hz

(2) 644.8 Hz

(3) 481.2 Hz

(4) 286.5 Hz

A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before and after the passing of the car is 11 : 9. If the speed of sound is v, the speed of the car is 

(1) $\frac{1}{10}v$

(2) $\frac{1}{2}v$

(3) $\frac{1}{5}v$

(4) v

A small source of sound moves on a circle as shown in the figure and an observer is standing on O. Let n₁, n₂ and n₃ be the frequencies heard when the source is at A, B, and C respectively. Then

(1) n₁ > n₂ > n₃

(2) n₂ > n₃ > n₁

(3) n₁ = n₂ > n₃

(4) n₂ > n₁ > n₃

A source emits a sound of frequency of 400 Hz, but the listener hears it to be 390 Hz. Then 

(1) The listener is moving towards the source

(2) The source is moving towards the listener

(3) The listener is moving away from the source

(4) The listener has a defective ear

A person carrying a whistle emitting continuously a note of \(272~\text{Hz}\) is running towards a reflecting surface with a speed of \(18~\text{km/hr}\). The speed of sound in air is \(345~\text{m/s}\). The number of beats heard by him is: 
1. \(4\)
2. \(6\)
3. \(8\)
4. \(3\)

If the pressure amplitude in a sound wave is tripled, then the intensity of sound is increased by a factor of

(1) 9

(2) 3

(3) 6

(4) $\sqrt{3}$

If the amplitude of the sound is doubled and the frequency reduced to one-fourth, the intensity of sound at the same point will be :

(1) Increased by a factor of 2

(2) Decreased by a factor of 2

(3) Decreased by a factor of 4

(4) Unchanged

Intensity level of a sound of intensity I is 30 dB. The ratio $\frac{I}{I_0}$ is (Where I₀ is the threshold of hearing) 

(1) 3000

(2) 1000

(3) 300

(4) 30

Quality of a musical note depends on :

(1) Harmonics present

(2) The amplitude of the wave

(3) Fundamental frequency

(4) The velocity of sound in the medium