Question

A boat that can travel at 4.0 km/h in still water crosses a river with a current of 2.0 km/h. At what angle must the boat be pointed upstream (that is, relative to its actual path) to go straight across the river? Draw a diagram

Answer 1

$$\cos a=\frac{v_r}{v_b}=\frac{2}{4}=0.5$$

$$a=60\degree$$