(a)[3]
On Fig. 6.1, indicate: (i) the centre of a compression using the letter C, (ii) the centre of a rarefaction using the letter R, (iii) one wavelength with a double-ended arrow.
(b)[1]
From the list, circle the value that gives the speed of sound in water: $15\,\text{m s}^{-1}$, $150\,\text{m s}^{-1}$, $1500\,\text{m s}^{-1}$, $15000\,\text{m s}^{-1}$, $150000\,\text{m s}^{-1}$, $1500000\,\text{m s}^{-1}$.
(c)[3]
Calculate the frequency of this sound wave by using your answer to (b).
(d)[2]
State and explain whether the sound in (c) counts as ultrasound.