Question

A man can swim with a speed of 4.0 km/h in still water. How long does he take to cross a river 1.0 km wide if the river flows steadily at 3.0 km/h and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

Answer 1

Speed of the man, v_m = 4 km/h
Width of the river = 1 km

Time taken to cross the river 

Speed of the river, v_r = 3 km/h
Distance covered with flow of the river = v_r × t