G L Mittal and TARUN MITTAL Solutions for Chapter: Doppler Effect, Exercise 3: FOR DIFFERENT COMPETITIVE EXAMINATIONS

A car is approaching a stationary policeman with a speed of $72 \mathrm{km}/\mathrm{h}$. To the policeman the frequency of the horn of the car appears to be $260 \mathrm{Hz}$. If the speed of sound is $332 \mathrm{m}/\mathrm{s}$, the actual frequency of the horn is :

A police car with a siren of frequency $8 \mathrm{kHz}$ is moving with a uniform velocity $36 \mathrm{km}/\mathrm{h}$  towards a tall building that reflects the sound waves. The speed of sound in air is $320 \mathrm{m}/\mathrm{s}$. The frequency of the siren heard by the car driver is :

An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency ?

A speeding motorcyclist sees traffic jam ahead of him. He slows down to $36 \mathrm{km} {\mathrm{h}}^{-1}$. He finds that traffic has eased and a car moving ahead of him at $18 \mathrm{km} {\mathrm{h}}^{-1}$ is honking at a frequency of $1392 \mathrm{Hz}$. If the speed of sound is $343 \mathrm{m} {\mathrm{s}}^{-1}$, the frequency of the honk as heard by him will be :

A whistle is whirled in a circle of radius $1.0 \mathrm{m}$, completing the circular path twice per second. The velocity of sound is $332 {\mathrm{ms}}^{-1}$. A person is standing outside the circle but in the plane of the circle. The ratio of the highest and the lowest frequency of the sound heard by him:

A siren placed on a railway platform emits sound of frequency $5 \mathrm{kHz}$. A passenger sitting in a train A moving towards the siren records the frequency of the siren as $5.5 \mathrm{kHz}$. Now, the passenger sitting in another train B, which is returning towards the siren, records the frequency of the siren as $6.0 \mathrm{kHz}$. Then, the ratio of the speeds of the trains B and is A:

A motorcycle starts from rest and accelerates along a straight path at $2 \mathrm{m}/{\mathrm{s}}^2$. At the starting point of the motorcycle there is a stationary electric siren. How far has the motorcycle gone when the driver hears the frequency of the siren at $94\%$ of its value when the motorcycle was at rest ? (speed of sound = $330 {\mathrm{ms}}^{-1}$)

A police car moving at $22$ $\mathrm{m}/\mathrm{s}$ chases a motorcyclist. The policeman sounds his horn at $176$ $\mathrm{Hz}$, while both of them move towards a stationary siren of frequency $165$ $\mathrm{Hz}$. If the motorcyclist does not hear any beat, then his speed is : (velocity of sound = $330$ $\mathrm{m}/\mathrm{s}$)