Source and Listener Moving in Different Lines

Q.

What Is Frequency Deviation In FM?

Q. Two tuning forks produce $4$ beats per second when they are sounded together. If both the forks are moving towards the observer in same direction with same speed $u$, the beat frequency heard becomes $5Hz$.
Consider the speed of sound to be $v$ $m{s}^{-1}$and choose the correct statements.

1. The value of $u$ is $\frac{v}{4}$
2. The value of $u$ is $\frac{v}{5}$
3. In the above situation, in addition to forks motion, if observer also begins to run with speed $u$ towards both the forks, the beat frequency he hears now is $5Hz$.
4. In the above situation, in addition to forks motion, if observer also begins to run with speed $u$ towards both the forks, the beat frequency he hears now is $6Hz$.

Q. A source of sound S is travelling at $\frac{100}{3}m/s$ along a road, towards a point A. When the source is 3 m away from A, a person standing at a point O on a road perpendicular to AS hears a sound of frequency v’. The distance of O from A at that time is 4m. If the original frequency is 640 Hz, then the value of v’ is (velocity of sound is 340 m/s)

1. 680 Hz
2. 720 Hz
3. 840 Hz
4. 620 Hz

Q. A vehicle, with a horn of frequency n, is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency n + n₁. Then n₁ is equal to (take velocity of sound in air as 330 m/s)

1. 
2. 
3. 
4. 

Q. A source is moving in a circle of radius $3m$ with constant angular velocity $\omega =5\text{rad/s}$. If the observer is at a distance $5m$ from the centre of circle, the time interval between maximum and minimum frequency received by the observer is

1. $\frac{\pi }{5}$
2. $\frac{2}{5}{\cos }^{-1}\left(\frac{3}{5}\right)$
3. $\frac{2}{5}{\sin }^{-1}\left(\frac{3}{5}\right)$
4. $\frac{2}{5}co{s}^{-1}\left(\frac{3}{4}\right)$

Q. Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/h and 36 km/h. If second car blows horn of frequency 280 Hz, then the frequency of horn heard by the driver of first car when the line joining the cars makes angle of ${45}^{\circ }$ with the roads, will be (velocity of sound is 330 m/s)

1. 321 Hz
2. 298 Hz
3. 289 Hz
4. 280 Hz

Q. A train is moving in an elliptical orbit in anticlockwise sense with a speed of 110 m/s. Guard is also moving in the given direction with same speed as that of train. The ratio of the length of major and minor axes is $\frac{4}{3}.$ Driver blows a whistle of 1900 Hz at P, which is received by guard at S. The frequency received by guard is (velocity of sound v = 330 m/s)

1. 1900 Hz
2. 1800 Hz
3. 1500 Hz
4. 2000 Hz

Q.

A train running at 108 km $h^{-1}$ towards east whistles at a dominant frequency of 600 Hz. Speed of sound in air is 340 m/s. What frequency will a passenger sitting near the open window hear ? (b) What frequency will a person standing near the track hear whom the train has just passed ? (c) A wind starts blowing towards east at a speed of 36 km $h^{-1}$. Calculate the frequencies heard by the passenger in the train and by the person standing near the track.

Q.

Figure (16-E7) shows two coherent sources $S_1$ and $S_2$ which emit sound of wavelength X in phase. The separation between the sources is $3\lambda$. A circular wire °f large radius is placed in such a way that $S_1,S_2$ lies in its plane and the middle point of $S_1,S_2$ is at the centre of the wire. Find the angular positions $\theta$ on the wire for which constructive interference takes place.

Q. Two trains $A$ and $B$ simultaneously start moving along parallel tracks from a station along same direction. A starts with constant acceleration $2{\text{m/s}}^2$ from rest while $B$ with the same acceleration but with initial velocity of $40\text{m/s}$. Twenty seconds after the start, passenger of $A$ hears whistle of $B$. If frequency of whistle is $1194\text{Hz}$ and velocity of sound in air is $322\text{m/s}$, then the frequency observed by the passenger is

1. $1086\text{Hz}$
2. $986\text{Hz}$
3. $886\text{Hz}$
4. $1186\text{Hz}$

Q. Source and observer start moving simultaneously along x and y-axis, respectively. The speed of source is twice the speed of observer, V₀. If the ratio of observed frequency to the frequency of the source is 0.75, find the velocity of sound.

1. $\frac{11}{\sqrt{5}}{V}_0$
2. $\frac{17}{\sqrt{5}}{V}_0$
3. $\frac{16}{\sqrt{5}}{V}_0$
4. $\frac{19}{\sqrt{5}}{V}_0$

Q.

A source emitting sound at frequency 4000 Hz, is moving along the Y-axis with a speed of $22m{s}^{-1}$. A listener is situated on the ground at the position (660 m, 0). Find the frequency of the sound received by the listener at the instant the source crosses the origin. Speed of sound in air $=330m{s}^{-1}$.

Q. The source $S_1$ is at rest. The observer and the source $S_2$ are moving toward $S_1$ as shown in the figure. The beat frequency heard by the observer if both the source have the frequency of $120Hz$ is (speed of sound is $330m/s$)

Q.

A signal wave of frequency $12kHz$ is modulated with a carrier wave of frequency $2.51MHz$. The upper and lower sideband frequencies are respectively

1. $2512kHz$and $2508kHz$

2. $2522kHz$and $2488kHz$

3. $2502kHz$ and $2498kHz$

4. $2522kHz$ and $2498kHz$

5. $2512kHz$ and $2488kHz$

Q. ntThe angular frequency of a fan increases from 30 rpm to 60 rpm in pi seconds. A dust particle is present at a distance of 20 cm from axis of rotation. The tanential acceleration of the particle in pi sec is?n

Q.

A boy riding on his bike is going towards east at a speed of $4\sqrt{2}m{s}^{-1}$. At a certain point he produces a sound pulse of frequency 1650 Hz that travels in air at a speed of $334m{s}^{-1}$. A second boy stands on the ground ${45}^{\circ }$ south of east from him. Find the frequency of the pulse as received by the second boy.

Q. A railway engine whistling at a constant frequency moves with a constant speed. It goes past a stationary observer beside the railway track. Which of the following graphs best represents the variation of frequency of sound $n$ heard by the observer with the time $t$ ?

[Assume, medium is stationary. Source and observer are collinear]

1. 
2. 
3. 
4. 

Q.

Two electric trains run at the same speed of 72 km/h along the same track and in the same direction with a separation of 2.4 km between them. The two trains simultaneously sound brief whistles. A person is situated at a perpendicular distance of 500 m from the track and is equidistant from the two trains at the instant of the whistling. If both the whistles were at 500 Hz and the speed of sound in air is 340 m/s, find the frequencies heard by the person.

Q. The difference between the apparent frequencies of a source of sound perceived by a stationary observer during its approach and recession is $2\%$ of the actual frequency of the source. If the speed of sound is $300\text{m/s}$, the speed of the source is

1. $12\text{m/s}$
2. $6\text{m/s}$
3. $1.5\text{m/s}$
4. $3\text{m/s}$

Q. A sound source $S$ is moving along a straight track with speed $v,$ and is emitting sound of frequency ${\nu }_0$ (see figure). An observer is standing at a finite distance, at the point $O$, from the track. The time variation of frequency heard by the observer is best represented by:
($t_o$ represents the instant when the distance between the source and observer is minimum)

1. 
2. 
3. 
4. 

Q. A stationary observer receives a sound from a sound of frequency $v_0$ moving with a constant velocity $v_s=30m/s.$ The apparent frequency varies with time as shown in figure. Velocity of sound v = 300 m/s. Then which of the following is incorrect?

1. The frequency-time curve corresponds to a source moving at an angle to the stationary observer.
2. The maximum value of apparent frequency is 1111 Hz.
3. The minimum value of apparent frequency is 889 Hz.
4. The natural frequency of source is 1000 Hz.

Q. A train moving at a speed of $30\text{m/s}$ has just completed a U-curve in a semi-circular track. The engine is at the forward end of the semi-circular part of the track while the last carriage is at the rear end of the semi-circular track. The driver blows a whistle of frequency $200\text{Hz}$. If the velocity of sound is $340\text{m/s}$, then the apparent frequency as observed by a passenger in the middle of the train is

1. $219\text{Hz}$
2. $188\text{Hz}$
3. $200\text{Hz}$
4. $181\text{Hz}$

Q. the apparent frequency of a note when listenermoves towards a stationary source with velocity 40m/s is 200Hzwhen he moves from the same source with same speed the apparent frequency of note is 160Hz. calculate velocity of sound in air

Q. A source of sound is emitting a waves of wavelength 40 cm in air. If this source starts moving towards east with a velocity one-fourth the velocity of sound then the apparent wavelength of sound in a direction opposite to that of source will be

1. 20 cm
2. 50 cm
3. 80 cm
4. 100 cm

Q. The velocity of sound in a gas in which two waves of wavelengths $50$ cm and $50.5$ cm produces $6$ beats per second is?

1. $303$ m/s
2. $332$ m/s
3. $296$ m/s
4. $228$ m/s

Q. Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/h and 36 km/h. If first car blows horn. of frequency 280 Hz, then the frequency of horn. heard by the driver of second car when line joining the car makes angle of 45 with the roads, will be

1. 298 Hz
2. 321 Hz
3. 280 Hz
4. 289 Hz

Q.

A boy riding on his bike is going towards east at a speed of $4\sqrt{2}m{s}^{-1}$. At a certain point he produces a sound pulse of frequency 1650 Hz that travels in air at a speed of 334$m{s}^{-1}$. A second boy stands on the ground 45${}^{\circ }C$ south of east from him. Find the frequency of the pulse as received by the second boy.

1. 1670

2. 1650

3. 1640

4. None of these

Q. A stationary source sends sound waves of the single wavelength. A wall approaches it with a velocity of $33\text{cm/sec}.$ The speed of sound waves in the medium is $330\text{m/sec},$ reflection of the waves on the wall brings about a change in wavelength by

1. $0.2\%$
2. $0.3\%$
3. $0.1\%$
4. $0.4\%$

Q. The source $S_1$ is at rest. The observer and the source $S_2$ are moving toward $S_1$ as shown in the figure. The beat frequency heard by the observer if both the source have the frequency of $120Hz$ is (speed of sound is $330m/s$)

Q. A train is moving in an elliptical orbit in anticlockwise sense with a speed of 110 m/s. Guard is also moving in the given direction with same speed as that of train. The ratio of the length of major and minor axes is $\frac{4}{3}.$ Driver blows a whistle of 1900 Hz at P, which is received by guard at S. The frequency received by guard is (velocity of sound v = 330 m/s)

1. 1900 Hz
2. 1800 Hz
3. 2000 Hz
4. 1500 Hz