Two identical tubes $A$ and $B$ are kept in air and water, respectively, as shown. If the fundamental frequency of $A$ is $f_0$, then the fundamental frequency of $B$ is

  

A tube of diameter d and of length $l$ unit is open at both ends. Its fundamental frequency of resonance is found to be ${\nu }_1$. The velocity of sound in air is $330 \mathrm{m} {\mathrm{s}}^{-1}$. One end of the tube is now closed. The lowest frequency of resonance of tube is now ${\nu }_2$. Taking into consideration the end correction $\frac{{\nu }_2}{{\nu }_1}$ is

An engine driver moving towards a wall with a velocity of $50 \mathrm{m} {\mathrm{s}}^{–1}$ emits a note of frequency $1.2 \mathrm{kHz}$. The frequency of note after reflection from the wall as heard by the engine driver when the speed of sound in air is $350 \mathrm{m} {\mathrm{s}}^{–1}$ is