$A$ tuning fork of frequency $512\, Hz$ makes $4$ beats per second with the vibrating string of a piano. The beat frequency decreases to $2$ beats per second when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was .... $Hz$

An observer while going on a scooter hears the sound of two sirens of the same frequency from two opposite directions. If he travels along the direction of one of the sirens,then he:

$A$ source of unknown frequency gives $4\, \text{beats/s}$ when sounded with a source of known frequency $250\, \text{Hz}.$ The second harmonic of the source of unknown frequency gives $5\, \text{beats/s}$ when sounded with a source of frequency $513\, \text{Hz}.$ The unknown frequency is .... $\text{Hz}$

$A$ vibrating tuning fork of frequency $n$ is placed near the open end of a long cylindrical tube. The tube has a side opening and is fitted with a movable reflecting piston. As the piston is moved through $8.75 \, cm$,the intensity of sound changes from a maximum to a minimum. If the speed of sound is $350 \, m/s$,then $n$ is .... $Hz$.

$A$ prong of a vibrating tuning fork is in contact with the water surface. It produces concentric circular waves on the surface of the water. The distance between five consecutive crests is $0.8 \ m$ and the velocity of the wave on the water surface is $56 \ m/s$. The frequency of the tuning fork is: (in $Hz$)

$A$ source of frequency $\nu$ gives $6 \text{ beats/second}$ when sounded with a source of frequency $200 \text{ Hz}$. The second harmonic of frequency $2\nu$ of the source gives $8 \text{ beats/second}$ when sounded with a source of frequency $420 \text{ Hz}$. The value of $\nu$ is (in $text{ Hz}$)