State whether the following statement is true or false:
The audible range of frequencies for human beings is $20 \, Hz - 20 \, kHz$.

Why do astronauts talk to each other through radio telephones?

$(a)$ What is reverberation? Write two ways of reducing reverberation.
$(b)$ Distinguish between tone and note.
$(c)$ With the help of a simple diagram,explain how defects in a metal block can be detected using ultrasound.

$A$ body vibrating with a time period of $5 \times 10^{-3} \text{ s}$ produces a wave travelling in a medium with a velocity of $1450 \text{ m s}^{-1}$. Calculate its wavelength and the frequency of vibration of the body.

$A$ key of a mechanical piano is struck gently and then struck again but much harder this time. In the second case,

State the relationship between frequency and time period of a wave. The wavelength of vibrations produced on the surface of water is $2 \, cm$. If the wave velocity is $16 \, m s^{-1}$, find its frequency and time period.