Crossing a river

To understand relative motion in a simple situation: a swimmer crossing a river.

(Figure 1) As shown, a swimmer wants to cross a river, from point A to point B. The distance d₁ (between A and C) is 200 m, the distance d₂ (between C and B) is 150 m, and the river’s speed v_r is 5.00 km/h. The swimmer's velocity relative to the water makes an angle of θ=45∘ with respect to AC.

Part A
The speed of a swimmer relative to a river’s speed To swim directly from A to B, what speed v_s, relative to the river’s speed, should the swimmer have?  
Express the swimmer's speed numerically to three significant figures in kilometers per hour.

Video Solution: