Question

What is the speed relative to the ground of a boat moving at 12 m/s relative to the river, which flows with 5 m/s right–angle to the boat's direction?

Answer 1

$\overrightarrow{v}_a=\overrightarrow{v}_r+\overrightarrow{v}_e$

$v_a=\sqrt{v_r^2+v_e^2}=\sqrt{12^2+5^2}=13(m/s)$