Infrasound can be heard by

$(a)$ What are the basic factors on which the speed of sound in a medium depends?
$(b)$ Why are sound waves called mechanical waves?
$(c)$ How will you differentiate a high-pitch sound from a low-pitch sound with the help of a graph?

What is a crest?

Why do astronauts talk to each other through radio telephones?

$A$ man stands between two high-rise buildings and blows a whistle. He hears two successive echoes after $0.4 \, s$ and $2.0 \, s$. Calculate the distance between the buildings. (Assume the speed of sound $v = 332 \, m/s$)

The pulse rate of a man is $80$ beats in one minute. Calculate its frequency. (in $ Hz$)