A river flows due south with a speed of 2.0 m/s. A man steers a motorboat across the river; his velocity relative to the water is 4 m/s due east. The river is 800 m wide. What is his velocity relative to the earth? Assume North as positive y-direction.
→vriver=−2^jm/s,→vman,river=4^im/s
→vmr=→vm−→vr
⇒→vm=→vmr+→vr
= 4^i−2^j