question_answer 13)

A man can swim with a speed of  in still water. How long does he take to cross the river 1 km wide, if the river flows steadily at  and he makes his strokes normal to the river current ? How far from the river does he go, when he reaches the other bank ?  

Answer:

 In Fig. 4.105,  and  represent the velocities of man and river. Clearly  is the resultant of these velocities. If the man begins to swim along AB, he will be deflected to the path AC by the flowing river.     Time taken to cover distance AC with velocity  will be same as the time taken to cover distance AB with velocity .  Time taken by the man to cross the river is . Distance through which the man goes down the river is .