## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

Let $v_b$ be the speed of the boat. Let $v_r$ be the speed of the river. We can set up two equations of the form $v = \frac{d}{t}$ $v_b+v_r = \frac{30~km}{3.0~hr} = 10~km/h$ $v_b-v_r = \frac{30~km}{5.0~hr} = 6~km/h$ We can subtract the second equation from the first equation. $2v_r = 4~km/h$ $v_r = 2~km/h$ The river is flowing at a speed of 2 km/h