A research hydrophone is suspended at rest in seawater and registers sounds emitted by a whale. The whale swims in a horizontal circle of radius 50m centred on the hydrophone, maintaining a constant speed of 3.0m⋅s−1. The whale’s call has a rest frequency of 150Hz.
(a) At the instant the whale is due east of the hydrophone and moving due north, indicate whether the frequency detected by the hydrophone is greater than, less than, or equal to 150Hz. Explain your reasoning in terms of components of velocity.
(b) After the whale has moved 45∘ counter-clockwise around the circle from the position described in part (a), determine whether the detected frequency is now greater than, less than, or equal to 150Hz. Support your answer with a qualitative explanation referring to the whale’s motion relative to the hydrophone.