Apparent Frequency:Source Moving

Q. The frequency of a radar is 780 MHz. After getting reflected from an approaching aeroplane, the apparent frequency is more than the actual frequency by 2.6 kHz. The aeroplane has a speed of

1. 2 km/s
2. 1 km/s
3. 0.5 km/s
4. 0.25 km/s

Q. A whistle emitting a sound of frequency 440 Hz is tied to a string of 1.5 m length and rotated with an angular velocity of 20 rad/s in the horizontal plane. Then the range of frequencies heard by an observer stationed at a large distance from the whistle will be (v = 330 m/s)

1. 400.0 Hz to 480.0 Hz
2. 403.3 Hz to 484.0 Hz
3. 400.0 Hz to 484.0 Hz
4. 403.3 Hz to 480.0 Hz

Q. A source emitting a sound of frequency f is placed at a large distance from an observer. The source starts moving towards the observer with a uniform acceleration ‘a’. Find frequency heard by the observer corresponding to the wave emitted just after the source starts. The speed of sound in medium is v.

1. 
   
2. 
3. 
   
4. 

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

1. 1333 Hz
2. 750 Hz
3. 1143 Hz
4. 857 Hz

Q. A source of sound is travelling with a velocity of 30 m/s towards a stationary observer. If actual frequency of source is 1000 Hz and the wind is blowing with velocity 20 m/s in a direction at ${60}^{\circ }$ with the direction of motion of source, then the apparent frequency heard by observer is (speed of sound is 340 m/s)

1. 1011 Hz
2. 1000 Hz
3. 1094 Hz
4. 1086 Hz

Q. Consider a source of sound S, and an observer/detector D. The source emits a sound wave of frequency $f_0$. The frequency observed by D is found to be

1. 
2. 
3. 
4. 

Q.

The horn of a car emits sound with a dominant frequency of 2400 Hz. What will be the apparent dominant frequency heard by a person standing on the road in front of the car if the car is approaching at 18.0 km/h? Speed of sound in air = 340 m/s.

1. 2374 Hz

2. None of these

3. 2436 Hz

4. 2400 Hz

Q.

A person riding a car moving at 72 km/h sounds a whistle emitting a wave of frequency 1250 Hz. What frequency will be heard by another person standing on the road (i) in front of the car (ii) behind the car? Speed of sound in air = 340 m/s.

1. 1328 Hz, 1181 Hz

2. 1620 Hz , 1080 Hz

3. None of these

4. 1250 Hz, 1181 Hz

Q. A train approaching a platform at a speed of 54 km/h sounds a whistle. An observer on the platform finds its frequency to be 1620 Hz. The train passes the platform keeping the whistle on and without slowing down. What frequency will the observer hear after the train has crossed the platform? The speed of sound in air = 332 m/s.

1. 1620 Hz

2. 1600 Hz

3. 1480 Hz

4. None of these

Q. In the figure shown, a source of sound of frequency 510 Hz moves with constant velocity = 20 m/s in the direction shown. The wind is blowing at a constant velocity = 20 m/s towards an observer who is at rest at point B. Corresponding to the sound emitted by the source at initial position A, the frequency detected by the observer is equal to (speed of sound relative to air is 330 m/s)

1. 510 Hz
2. 500 Hz
3. 525 Hz
4. 550 Hz