In figure, speed of boat v0=4km∕h, speed of river vr=3km∕h and width of river =2km.
The magnitude of the resultant velocity is vres =√vb2+v12=√32+42 ⇒vres. =5km∕h Since, horizontal component (speed of boat) remain constant, so time taken in travelling 2km distance is t=
2
4
=0.5h In 0.5h, distance travelled by object with resultant velocity D=vres ×t=5×0.5=2.5km