Final answer:
The resultant velocity of the goose flying due south at 20 km/hr against a 15 km/hr wind from the north is 5 km/hr due south. This is determined by vector subtraction due to opposite directions of travel and wind.
Step-by-step explanation:
When analyzing the goose's resultant velocity, we need to consider the vectors of its own flight speed and the wind speed. The goose is flying due south at 20 km/hr, and there is a wind coming from due north at 15 km/hr. Vector addition requires that we subtract the goose's southward velocity vector by the northward wind velocity vector, as they are in opposite directions.
The calculation is as follows:
Goose's velocity (due South): 20 km/hr
Wind's velocity (due North): 15 km/hr
Resultant velocity = Goose's velocity - Wind's velocity = 20 km/hr - 15 km/hr = 5 km/hr due South
Therefore, the goose's resultant velocity is 5 km/hr due South, which corresponds to option A).