An observer moves towards a stationary source of sound with a velocity one fifth of the velocity of the sound. What is the percentage increment in apparent frequency?
Ans: \(\frac{\Delta\nu}{\nu}\times100=20\%\).
Find: the velocity of the source of sound when the frequency appears to be (i) Double (ii) Half of the original frequency to a stationary observer. Velocity of the sound \(=330\frac{m}{s}\).
Ans: \(v_{source}=-330\frac{m}{s}\).
If the pitch of the sound of a source appears to be dropped by \(15\%\) to a moving person, then determine the velocity of motion ofthe person. Take: Velocity of the sound \(=340\frac{m}{s}\).
Ans: \(v_{person}=51\frac{m}{s}\).
A siren emitting a sound of frequency \(1000\) vibrations per second is moving with a speed of \(10\frac{m}{s}\). What will be the frequency of the sound which an observer will hear when (i) The siren is moving towards him. (ii) Siren is moving away from him. (Velocity of sound in air\(=340\frac{m}{s}\)).
Ans: (i) \(1030Hz\) and (ii) \(971Hz\).
An observer moving towards a wall at \(20\frac{m}{s}\), hears a sound from a source at some distance behind him directly as well as after reflection from the wall. Deduce the beats frequency between these two sounds. Taking: True frequency as \(580Hz\) and \(340\frac{m}{s}\).
Ans: \(68\).
A train at the outer signal of a railway station blows a whistle of frequency \(400Hz\). Calculate: The frequency of the whistle for an observer at the platform when the train (i) Approaches platform with a speed of \(20\frac{m}{s}\). (ii) Recedes from the platform with a speed \(20\frac{m}{s}\)? Take: Velocity of sound \(=340\frac{m}{s}\).
Ans:(i) \(425Hz\) and (ii) \(377.8Hz\).
An observer standing on a railway crossing receives frequencies of \(2.2KHz\) and \(1.8KHz\) when the train approaches and recedes from the observer. Find: the velocity of train. Velocity of sound is \(300\frac{m}{s}\).
Ans: \(v_{train}=30\frac{m}{s}\).
A railway engine and a car are moving on parallel tracks, with speed of \(144\frac{km}{h}\) and \(72\frac{km}{h}\) respectively. The engine is continuously sounding a whistle of frequency \(500Hz\). The velocity of sound is \(340\frac{m}{s}\). calculate: the frequency of sound heard in the car when (i) The car and the engine are approaching each other. and (ii) The two are moving away from each other.
Ans:(i) \(\nu’=600Hz\) and (ii) \(\nu”=421Hz\).
Find: the velocities of the source of sound, when the frequency appears to be (i) Double and (ii) Half of the original frequency to a stationary observer. Velocity of sound \(=330\frac{m}{s}\).
(i) \(v_{s}=165\frac{m}{s}\) and (ii) \(v_{s}’=-330\frac{m}{s}\).
A rocket is moving at a speed of \(200\frac{m}{s}\) towards a stationary target. While moving, it emits a sound wave of frequency \(1000Hz\). Same of the sound reaching the target gets reflected back to the rocket as an echo. Calculate: (a) The frequency of the sound wave as detected by a detector attached to the target and (b) The frequency of the the echo as detected by a detector attached to the rocket.
Ans:(a) \(\nu’=2538.5Hz\) and (b) \(\nu”=4077Hz\).
