Listener and Source Moving

Q.

Why there is no frequency in DC?

Q.

A police car moving at 22 m/s, chases a motorcyclist. The police man sounds his horn at 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of the motorcycle, if it is given that he does not observe any beats.

1. 33 m/s

2. 22 m/s

3. Zero

4. 11 m/s

Q. A siren placed at a railway platform is emitting sound of frequency 5 kHz. A passenger sitting in a moving train A records a frequency of 5.5 kHz while the train approaches the siren. During his return journey in a different train B he records a frequency of 6.0 kHz while approaching the
same siren. The ratio of velocity of train B to that of train A is

1. $\frac{242}{252}$
2. $2$
3. $\frac{5}{6}$
4. $\frac{11}{6}$

Q. A band playing music at frequency f is moving towards a wall at a speed $v_b$. A motorist is following the band with a speed $v_m$. If v is the speed of sound, the expression for the beat frequency heard by the motorist is

1. $\frac{v+v_m}{v+v_b}f$
2. $\frac{v+v_m}{v-v_b}f$
3. $\frac{2v_b(v+v_m)}{v^2-v_b^2}f$
4. $\frac{2v_m(v+v_b)}{v^2-v_m^2}f$

Q. An isotropic stationary source is emitting waves of frequency n and wind is blowing due north. An observer A is on north of the source while observer B is on south the source. If both the observers are stationary, then

1. frequency received by A is greater than n
2. frequency received by B is less than n
3. frequency received by A equals to that received by B
4. frequencies received by A and B cannot be calculated unless velocity of waves in still air and velocity of wind are known

Q. A siren placed at a railway platform is emitting sound of frequency 5 kHz. A passenger sitting in a moving train A records a frequency of 5.5 kHz while the train approaches the siren. During his return journey in a different train B he records a frequency of 6.0 kHz while approaching the
same siren. The ratio of velocity of train B to that of train A is

1. $\frac{242}{252}$
2. $2$
3. $\frac{5}{6}$
4. $\frac{11}{6}$

Q. A police car moving at 22 m/s chases a motorcyclist. The police man sounds his horn of frequency 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of motorcyclist if it is given that he does not hear any beat (speed of sound in air is 330 m/s)

1. 33 m/s
2. 22 m/s
3. 11 m/s
4. zero

Q.

A source of sound emitting a note of frequency 200 Hz moves towards an observer with a velocity $v$ equal to the velocity of sound. If the observer also moves away from the source with the same velocity $v$, the apparent frequency heard by the observer is

1. 50 Hz
2. 100 Hz
3. 150 Hz
4. 200 Hz

Q. A sound wave of frequency n travels horizontally to the right with speed c. It is reflected from a broad wall moving to the left with speed v. The number of beats heard by a stationary observer to the left of the wall is

1. zero
2. $\frac{n(c+v)}{c-v}$
3. $\frac{nv}{c-v}$
4. $\frac{2nv}{c-v}$

Q. A police car moving at 22 m/s chases a motorcyclist. The police man sounds his horn of frequency 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of motorcyclist if it is given that he does not hear any beat (speed of sound in air is 330 m/s)

1. 33 m/s
2. 22 m/s
3. 11 m/s
4. zero

Q. A boy is walking away from a wall at a speed of 1.0 m/s in a direction at right angles to the wall. The boy blows a whistle steadily. An observer towards whom the boy is moving hears 4 beats/s. If the speed of sound is 340 m/s, the frequency of whistle is

1. 480 Hz
2. 680 Hz
3. 840 Hz
4. 1000 Hz

Q. A band playing music at frequency f is moving towards a wall at a speed $v_b$. A motorist is following the band with a speed $v_m$. If v is the speed of sound, the expression for the beat frequency heard by the motorist is

1. $\frac{v+v_m}{v+v_b}f$
2. $\frac{v+v_m}{v-v_b}f$
3. $\frac{2v_b(v+v_m)}{v^2-v_b^2}f$
4. $\frac{2v_m(v+v_b)}{v^2-v_m^2}f$

Q. A sound wave of frequency f travels horizontally to the right. It is reflected from a large vertical plane surface moving to left with a speed v. The speed of sound in medium is c. The incorrect statement is

1. The number of wave striking the surface per second is $f\frac{(c+v)}{c}$
2. The wavelength of reflected wave is $\frac{c(c-v)}{f(c+v)}$
3. The frequency of reflected wave is $\frac{f(c+v)}{(c-v)}$
4. The number of beats heard by a stationary listener to the left of the reflecting surface is $\frac{vf}{(c-v)}$