A source of sound and listener are approaching each other with a speed of 40 m/s. The apparent frequency of note produced by the source is 400 cps. Then, its true frequency (in cps) is (velocity of sound in air = 360 m/s) 

(1) 420

(2) 360

(3) 400

(4) 320

A man sitting on a moving train hears the whistle of the engine. If the frequency of the whistle is 600 Hz, then:

1. the apparent frequency as heard by him is smaller than 600 Hz.

2. the apparent frequency is larger than 600 Hz.

3. the frequency as heard by him is 600 Hz.

4. None of the above

A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is f₁. If the train’s speed is reduced to 17 m/s, the frequency registered is f₂. If the speed of sound is 340 m/s then the ratio f₁/f₂ is 

(1) 18/19

(2) 1/2

(3) 2

(4) 19/18

If source and observer both are relatively at rest and if speed of sound is increased then frequency heard by observer will :

(1) Increases

(2) Decreases

(3) Can not be predicted

(4) Will not change

A source and an observer move away from each other with a velocity of 10 m/s with respect to ground. If the observer finds the frequency of sound coming from the source as 1950 Hz, then actual frequency of the source is (velocity of sound in air = 340 m/s) 

(1) 1950 Hz

(2) 2068 Hz

(3) 2132 Hz

(4) 2486 Hz

A whistle revolves in a circle with an angular speed of 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer, which is far away from the centre in the same plane ? $(v_{sound} = 340 m/s)$

(1) 333 Hz

(2) 374 Hz

(3) 385 Hz

(4) 394 Hz

A Siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s, frequency of the sound to be heard by the listener is (take velocity of sound as 330 m/s)

(1) 733.3 Hz

(2) 644.8 Hz

(3) 481.2 Hz

(4) 286.5 Hz

A source emits a sound of frequency of 400 Hz, but the listener hears it to be 390 Hz. Then 

(1) The listener is moving towards the source

(2) The source is moving towards the listener

(3) The listener is moving away from the source

(4) The listener has a defective ear

Two waves having sinusoidal waveforms have different wavelengths and different amplitudes. They will be having :

(1) Same pitch and different intensity

(2) Same quality and different intensity

(3) Different quality and different intensity

(4) Same quality and different pitch

The ends of a stretched wire of length L are fixed at x = 0 and x = L. In one experiment, the displacement of the wire is $y_1=A\sin (\pi x/L)\sin \omega t$ and energy is E₁, and in another experiment its displacement is $y_2=A\sin (2\pi x/L)\sin 2\omega t$ and energy is E₂. Then :

(1) E₂ = E₁

(2) E₂ = 2E₁

(3) E₂ = 4E₁

(4) E₂ = 16E₁