Julia can swim at 3.5 km/hr in still water. She attempts to head straight north across a river with a current

flowing at 1.2 km/hr [W]. What is her resultant velocity?

- - Relative to the water, Julia's velocity is 3.5 km/hr to the north.

- - Relative to the shore, her velocity is

(3.5 km/hr north) + (1.2 km/hr west)

= √ (3.5² + 1.2²) arctan (3.5/1.2) north of west

= √13.69 arctan (2.91666 ...) north of west

= 3.7 km/hr towards 71° north of west.