The echo of a gun shot is heard $8 \, s$ after the gun is fired. How far from the shooter is the surface that reflects the sound (in $, m$)? (Velocity of sound in air $= 350 \, m/s$)

The wavelength of sound waves in hydrogen gas corresponding to the lower limit of audibility is ........ $m$ (speed of sound in hydrogen gas is about $1350 \, m/s$).

The speed of sound waves in a fluid depends upon:

Earthquakes generate sound waves inside the earth. Unlike a gas,the earth can experience both transverse $(S)$ and longitudinal $(P)$ sound waves. Typically,the speed of $S$ wave is about $4.0 \; km/s$,and that of $P$ wave is $8.0 \; km/s$. $A$ seismograph records $P$ and $S$ waves from an earthquake. The first $P$ wave arrives $4 \; min$ before the first $S$ wave. Assuming the waves travel in a straight line,at what distance (in $km$) does the earthquake occur?

Which of the following statements is wrong?

An earthquake generates both transverse $S$ and longitudinal $P$ waves in the earth with speeds $4.5 \,km/s$ and $8.0 \,km/s$, respectively. $A$ seismograph records that the first $P$-wave arrives $3.5 \,min$ earlier than the first $S$-wave. From the seismograph, the epicentre of the earthquake is located at a distance of: (in $\,km$)