The temperature at which the speed of sound in air becomes double of its value at $27^\circ C$ is ... $^\circ C$

$A$ person in front of a mountain is beating a drum at the rate of $40$ per minute and hears no distinct echo. If the person moves $90 \, m$ closer to the mountain,he has to beat the drum at $60$ per minute to not hear any distinct echo. The speed of sound is .............. $ms^{-1}$.

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

$A$ wave with a wavelength of $0.60 \ cm$ is produced in air and it travels at a speed of $300 \ ms^{-1}$. This wave is classified as:

$A$ person standing between two parallel cliffs fires a gun and hears two echoes, the first echo after $1$ second and the second echo after $3$ seconds. The distance between the two cliffs is (The velocity of sound = $330$ m/s). (in $m$)

The velocity of sound in air at $20^{\circ} C$ and $1 \text{ atm}$ pressure is $344.2 \text{ m/s}$. At $40^{\circ} C$ and $2 \text{ atm}$ pressure, the velocity of sound in air is approximately: (in $\text{ m/s}$)