Two factories are sounding their sirens at 800 Hz. A man goes from one factory to the other at a speed of 2 m/s. The velocity of the sound is 320 m/s. The number of beats heard by the person in one second will be:


Correct option is



When the man is approaching the factory:


When the man is going away from the factory,




At what temperature the speed of sound in oxygen will be same as that in nitrogen at 14oC? The molecular weights of oxygen and nitrogen are 32 and 28 respectively.


A wave whose amplitude is 0.07 m and frequency is 400 hertz travels in a medium with a velocity of 300 m/s. Determine the displacement equation of oscillation at a distance x metre from the source due to this wave.


The intensity of a sound wave gets reduced by 20% on passing through a slab. The reduction in intensity on passage through two such consecutive slabs is:


A is singing a note and at the same time B is singing a note with exactly one-eighth the frequency of the note of A. The energies of the two sounds are equal. The amplitude of the note of B is:


A twofold increase in the intensity of a wave implies an increase of:


An increase in intensity level of one decibel implies an increase in intensity of:


An observer is moving with velocity v0 towards a stationary sound source emitting waves of frequency n. If v is the velocity of sound waves, then the wavelength of the sound waves as detected by the observer will be:


A rocket ship is receding from the earth at a speed of 0.2 c. The ship emits the signal of frequency  The apparent frequency to an observer on the surface of the earth is:


A source of sound is moving with a velocity 50 m/s towards a stationary observer. The observer measured the frequency of the source as 1000 Hz. What will be the apparent frequency of the source when it is moving away from the observer after crossing him? The velocity of the sound in the medium is 350 m/s.


Two trains, one coming towards and another going away from an observer both at 4 m/s produce a whistle simultaneously of frequency 300 Hz. Find the number of beats produced?