A ship is travelling due east at 30 km/hr and a boy runs across the deck in a south west direction at 10 km/hr. Find the velocity of the boy
relative to sea.

Vr = 20 [km/h]

Explanation:

In order to solve this problem, we have to add the relative velocities. We must remember that velocity is a vector, therefore it has magnitude and direction. We will take the sea as the reference measurement level.

Let's take the direction of the ship as positive. Therefore the boy moves in the opposite direction (Negative) to the reference level (the sea).

c)as speed changes, wavelength and frequency change.

everything changes!