Physics: Sound Wave MCQs

velocity of sound in air is 

A tuning fork of frequency 480Hz . Produces 10 beats per second when sounded with a vibrating sonometer string. What must have been the frequency of the string if a slight increase in tension produces beats per second then before?

When a source is giving away from a stationary observer with a velocity equal to that of sound in air,then the frequency hear by the observer will be 

ten tuning fork are arranged in arranged in increasing order of frequency in such a way that any two nearest tuning forks produces 4 beats per second . The highest frequency is twice that of the lowest .possible highest and lowest frequencies are 

If X=a sin (ωt+π/6) and x’=acosωt, then what is the phase difference between the two waves