A train moves towards a stationary observer at a speed of 34 m/s. The train sounds a whistle and its frequency registered is $f_1$. If the train's speed is reduced to 17 m/s, the frequency registered is $f_2$. If the speed of sound is 340 m/s , then the ratio $\frac{f_1}{f_2}$ is

1. $\frac{18}{19}$

2. $\frac{1}{2}$

3. 2

4. $\frac{19}{18}$

A man sitting on a moving train hears the whistle of the engine. If the frequency of the whistle is 600 Hz, then:

1. the apparent frequency as heard by him is smaller than 600 Hz.

2. the apparent frequency is larger than 600 Hz.

3. the frequency as heard by him is 600 Hz.

4. None of the above

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

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 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

An observer moving at a velocity of 20 m/s is moving away from a source moving at a speed of 10 m/s towards the observer.
If the frequency of the source is 'f', then find the frequency observed by the observer is: ( $v_{sound} = 330 m/s$ )

1. $\frac{32}{31}f$

2. $\frac{47}{23}f$

3. $\frac{31}{32}f$

4. f

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

The driver of a car travelling at a speed of 30 m/s towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 m/s, the frequency of reflected sound as heard by the driver is:

1. 550 Hz

2. 555.5 Hz

3. 720 Hz

4. 500 Hz