[العباس]

Solution

a.

Since the vectors and are perpendicular (see Figure 3-18), the magnitude of can be determined by using the Pythagorean theorem:



Thus, the boat moves at a speed of 4.5 m/s with respect to an observer on shore. The direction of the boat relative to the shore is given by the angle in the drawing:




b.

The time t for the boat to cross the river is