Find the wavelength of a sound wave of frequency $4.2 \text{ MHz}$ travelling with a speed of $1.7 \text{ km/s}$.

The speed of a longitudinal wave in a metallic bar is $400 \ m/s$. If the density and Young's modulus of the bar material are increased by $0.5\%$ and $1\%$ respectively,then the speed of the wave is changed approximately to . . . . . . $m/s$.

The mass of one mole of a gas is $22.4 \times 10^{-3} \ kg$ and its specific heat ratio is $1.6$. The speed of sound in the gas at $STP$ is nearly: (in $m/s$)

What is the ratio of the velocity of sound in hydrogen $\left(\gamma=\frac{7}{5}\right)$ to that in helium $\left(\gamma=\frac{5}{3}\right)$ at the same temperature? (Molecular weight of hydrogen and helium is $2$ and $4$ respectively)

$A$ source $S$ of frequency $f_0$ and an observer $O$,moving with speeds $v_1$ and $v_2$ respectively,are moving away from each other. When they are separated by a distance $a$ at $t = 0$,a pulse is emitted by the source. This pulse is received by $O$ at time $t_1$. Then $t_1$ is equal to:

$A$ sound wave of frequency $v \text{ Hz}$ initially travels a distance of $1 \text{ km}$ in air. Then,it gets reflected into a water reservoir of depth $600 \text{ m}$. The frequency of the wave at the bottom of the reservoir is $(V_{\text{air}} = 340 \text{ m/s}, V_{\text{water}} = 1484 \text{ m/s})$