A Boat having a speed of 5 km per hour in stillwater crosses a river of width 1 km along the shortest possible path in 15 minutes the speed of the river in kilometre per horse

let the velocity of the river be x. the velocity of the river will be in the horizontal direction

velocity of boat in still water is 5km/hr. As the width of the river is 1 km and time taken by the boat to cross the river along the shortest path is 15 min therefore the velocity of the boat is=  1*60/15= 4km/hr

 according to the figure the velocity of the river is along  AB . By applying triangle law of vector addition the value of AB comes to be 3km/hr

Regards

Arun (askIITians forum expert)