An observer starts moving with uniform acceleration towards a stationary sound source of frequency ${\mathrm{f}}_0$. As the observer approaches the source, the apparent frequency f heard by the observer varies with time t as

1.		2.
3.		4.

A bus is moving with a velocity of 5 m/s towards a huge wall. The driver sounds a horn at a frequency of 165 Hz. If the speed of sound in air is equal to 335 m/s, the number of beats heard per second by a passenger on the bus will be:

A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz. If the velocity of the sound in the medium is 350 m/s, then what will be the apparent frequency of the source when it is moving away from the observer after crossing him?

1. 750 Hz

2. 857 Hz

3. 1143 Hz

4. 1333 Hz

A source of sound with a frequency n = 2000 Hz moves along a line at right angles to the wall with a velocity ${\mathrm{v}}_{\mathrm{s}}=0.33$ m/s. Two stationary detectors, ${\mathrm{D}}_1 \mathrm{and} {\mathrm{D}}_2$ , are placed on the path of the source as shown in the figure. The velocity of sound in air is v = 330 m/s. Then:
                  
1. Only ${\mathrm{D}}_1$ records beats

2. Only ${\mathrm{D}}_2$ records beats

3. Both ${\mathrm{D}}_1 \mathrm{and} {\mathrm{D}}_2$ record beats

4. Neither ${\mathrm{D}}_1 \mathrm{nor} {\mathrm{D}}_2$ record beats

A car with a siren is moving towards a hill at a speed of 108 km/h.  A person is standing at the foot of the hill. The frequency observed by a person is: (frequency of siren is 600 Hz, velocity of sound is 330 m/s)

1. 720 Hz

2. 660 Hz

3. 600 Hz

4. 630 Hz

A train moves towards a stationary observer at 50 m/s. The train sounds a whistle and its frequency is registered by the observer as ${\mathrm{f}}_1$. If the train's speed is increased by 25 m/s, the frequency registered is ${\mathrm{f}}_2$. If the speed of sound is 300 m/s, then ${\mathrm{f}}_1$:${\mathrm{f}}_2$ is:

1. 3:5

2. 5:7

3. 7:9

4. 9:10

A train, standing at the outer signal of a railway station blows a whistle of frequency \(400\) Hz in still air. What is the frequency of the whistle for a platform observer when the train approaches the platform with a speed of \(10\) m/s?
(Speed of sound\(=340\) m/s)
1. \(512 \) Hz
2. \(312 \) Hz
3. \(412\) Hz
4. \(400\) Hz

A SONAR system fixed in a submarine operates at a frequency 40.0 kHz. An enemy submarine moves towards the SONAR with a speed of 360 km/h. What is the frequency of sound reflected by the enemy submarine? (the speed of sound in water to be 1450 m/sec.)

(1) 44.2 kHz

(2) 45.9 kHz

(3) 43.7 kHz

(4) 46.1 kHz

A bat is flitting about in a cave, navigating via ultrasonic beeps. Assume that the sound emission frequency of the bat is 40 kHz. During one fast swoop directly toward a flat wall surface, the bat moves at 0.03 times the speed of sound in the air. What frequency does the bat hear reflected off the wall?

1. 41.27 kHz

2. 42.67 kHz

3. 41.23 kHz

4. 42.47 kHz

A policeman buzzes a whistle of frequency 420 Hz. A car with an audio recorder is moving towards the policeman with a speed of 72 km/h, recording a frequency of ${\mathrm{v}}_1$. If, after crossing, it records the frequency of ${\mathrm{v}}_2$, then ${\mathrm{v}}_1$- ${\mathrm{v}}_2$  is: (Velocity of sound is 300 m/s)

1. $\sqrt{2}$ Hz

2. 20 Hz

3. 28 Hz

4. 56 Hz