A source of sound moves away with the velocity of sound from a stationary observer. The frequency of the sound heard by the observer:

1. remains the same

2. is doubled

3. is halved

4. becomes infinity
 

If a sound source of frequency n approaches an observer with velocity v/4 and the observer approaches the source with velocity v/5, then the apparent frequency heard will be-

1.  (5/8)n

2.  (8/5)n

3.  (7/5)n

4.  (5/7)n

Two cars moving in opposite directions approach each other with speed of 22m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340m/s]

1. 350Hz

2. 361Hz

3. 411Hz

4. 448Hz

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of $15{\mathrm{ms}}^{-1}$. The frequency of sound that the observer hears in the echo reflected from the cliff will be:
(Take, velocity of sound in air=$330$ ${\mathrm{ms}}^{-1}$)
1. 800 Hz
2. 838 Hz
3. 885 HZ
4. 765 Hz

A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 ms^-1 at an angle of 60° with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound to air 330 ms^-1), is

1. 100 Hz
 

2. 103Hz
 

3. 106 Hz
 

4. 97 Hz

A speed motorcyclist sees a traffic jam ahead of him. He slows down to 36km/h. He finds that traffic has eased and a car moving in front of him at 18km/h is honking at a frequency of 1392Hz. If the speed of sound is 343m/s, the frequency of the honk as heard by him will be 
1. 1332Hz
2. 1372Hz
3. 1412Hz
4. 1454Hz 

A train moving at a speed of 220 ${\mathrm{ms}}^{-1}$ towards a stationary object, emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as an echo. The frequency of the echo as detected by the driver of the train is
(speed of sound in air is 330 ${\mathrm{ms}}^{-1}$)
1. 3500Hz
2. 4000Hz
3. 5000Hz
4. 3000Hz

The harmonics which are present in a pipe open at one end are :

1. Odd harmonics

2. Even harmonics

3. Even as well as odd harmonics

4. None of these

A source of sound of frequency 450 cycles/sec is moving towards a stationary observer with 34 m/sec speed. If the speed of sound is 340 m/sec, then the apparent frequency will be 

(1) 410 cycles/sec

(2) 500 cycles/sec

(3) 550 cycles/sec

(4) 450 cycles/sec

The frequency of a whistle of an engine is 600 cycles/sec is moving with the speed of 30 m/sec towards an observer. The apparent frequency will be (velocity of sound = 330 m/s) 

(1) 600 cps

(2) 660 cps

(3) 990 cps

(4) 330 cps