When a car is approaching the observer, the frequency of horn is $$100 \mathrm{~Hz}$$. After passing the observer, it is $$50 \mathrm{~Hz}$$. If the observer moves with the car, the frequency will be $$\frac{x}{3} \mathrm{~Hz}$$ where $$x=$$ ________________.
Two waves executing simple harmonic motions travelling in the same direction with same amplitude and frequency are superimposed. The resultant amplitude is equal to the $$\sqrt3$$ times of amplitude of individual motions. The phase difference between the two motions is ___________ (degree).
An observer is riding on a bicycle and moving towards a hill at $$18 \,\mathrm{kmh}^{-1}$$. He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is $$640 \mathrm{~Hz}$$ and velocity of the sound in air is $$320 \mathrm{~m} / \mathrm{s}$$, the beat frequency between the two sounds heard by observer will be _____________ $$\mathrm{Hz}$$.
An employee of a factory moving away from his workplace by a car listens to the siren of the factory. He drives the car at the speed of 72 kmh$$-$$1 in the direction of wind which is blowing at 72 kmh$$-$$1 speed. Frequency of siren is 720 Hz. The employee hears an apparent frequency of ____________ Hz.
(Assume speed of sound to be 340 ms$$-$$1)