Question

A man who can swim with 2km/hr in still water wants to cross a river flowing at 1 km/hr to reach the directly opposite end. In which direction should he try to swim?

Answer 1

Answer:

Explanation:

given, 

speed of man, Vm = 3km/hr

speed of river, Vr = 2km/hr

angle which the man makes with the direction of motion of river = 120

The resultant velocity of man can be calculated by the parallelogram law of vectors as,

angle between Vr and VR

now time required to cross the river = OB/VR

in trianle ABO, angleAOB = 90o - 79o = 11o

so, OB = AO/cos11o =  0.5/0.981 = 0.509

so time required = 0.509/2.6 = 0.196hr = 0.196x60x60 = 705.6s

 

Now the point  where he will reach is B, and the distance of  B from A = AB = AOtan11 =  0.097km 

                                                                                                                                          = 0.097x1000= 97m