$A$ man is standing between two parallel cliffs and fires a gun. If he hears the first and second echoes after $1.5 \, s$ and $3.5 \, s$ respectively,the distance between the cliffs is .... $m$ (Velocity of sound in air $= 340 \, ms^{-1}$)

The figure represents the instantaneous picture of a longitudinal harmonic wave travelling along the negative $x$-axis. Identify the correct statement$(s)$ related to the movement of the points shown in the figure. The points of maximum rarefaction are

Which of the following waves is used in sonography?

$v_1$ and $v_2$ are the velocities of sound at the same temperature in two monoatomic gases of densities $\rho_1$ and $\rho_2$ respectively. If $\frac{\rho_1}{\rho_2} = \frac{1}{4}$,then the ratio of velocities $v_1$ and $v_2$ will be

$A$ $SONAR$ (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a $SONAR$,the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be $77.0\; s$. What is the distance of the enemy submarine (in $; km$)? (Speed of sound in water $= 1450\; m/s$)

$A$ hospital uses an ultrasonic scanner to locate tumours in a tissue. The operating frequency of the scanner is $4.2 \, MHz$. The speed of sound in a tissue is $1.7 \, km/s$. The wavelength of sound in the tissue is close to: