Reflection of Sound Waves

Q. In Kundt's tube experiment, a metal rod of length $2\text{m}$ and density $8{\text{g/cm}}^3$ clamped at middle gives dust heaps in a Kundt's tube at intervals of $10\text{cm}$. Calculate the Young's modulus of the material of rod. The speed of sound, in the gas is $360\text{m/s}$.

1. $2.12\times {10}^{11}{\text{N/m}}^2$
2. $2.12\times {10}^{10}{\text{N/m}}^2$
3. $4.14\times {10}^{11}{\text{N/m}}^2$
4. $4.14\times {10}^{10}{\text{N/m}}^2$

Q. A sound signal is simultaneously sent in air and water from a boat on a river. The echo of sound returned by the river bed is heard is $4\text{s}$, while the echo returned by the aeroplane is heard in $8\text{s}$. Find the distance between the aeroplane and the river bed.

[velocity of sound in air = $350\text{m/s}$, velocity of sound in water = $1500\text{m/s}$]

1. $4.4\text{km}$
2. $6.4\text{km}$
3. $8.8\text{km}$
4. $13.4\text{km}$