The speed of sound is $310 \, m s^{-1}$. $A$ person fires a gun and the echo is heard after $1.5 \, s$. Calculate the distance of the person from the cliff from which the echo takes place. (in $, m$)

$(i)$ How do bats make use of ultrasonic waves to catch their prey? Explain.
$(ii)$ $A$ radar signal is reflected by an aeroplane and is received $2 \times 10^{-5} \text{ s}$ after it was sent. If the speed of these waves is $3 \times 10^{8} \text{ m s}^{-1}$,how far is the aeroplane?

$(a)$ Why are sound waves called mechanical waves? List two practical applications of reflection of these waves.
$(b)$ $A$ stone is dropped from the top of a tower $125 \ m$ high into a pond of water at the base of the tower. When is the splash heard at the top? $(g = 10 \ m s^{-2}$ and speed of sound $= 340 \ m s^{-1})$

For hearing the loudest ticking sound of the clock,find the angle $x$ in the figure. (in $^o$)

$(a)$ Briefly mention three uses of ultrasound in the field of medicine.
$(b)$ $A$ ship which is stationary is at a distance of $2800 \ m$ from the sea-bed. The ship sends an ultrasound signal to the sea-bed and its echo is heard after $4 \ s$. Find the speed of sound in water.

Which of the above two graphs $(a)$ and $(b)$ representing the human voice is likely to be the male voice? Give reason for your answer.