Question

A river 500m wide flows at the speed of 4km/h. A swimmer who can swim at 8km/h in still water, wishes to cross the river straight.
(i). Along what direction must he strike the river?

Answer 1

Explanation:

Since the river is flowing at 8kmph assuming he takes x hrs

In x hrs , the distance he swims is x*10

Extra distance due to river flow is x*8

0.6 ,x*10 (hypotenuse), x*8 (extra distance)

(x*10)^2-(x*8)^2=0.6^2

100x^2-64x^2=0.36

36x^2=36/100

x=1/10

In 1/10 th hour he crosses the river . Total distance is 1000 meters

The extra distance(along with river) he travels due to river speed is 8km/0.1=800 meters

The angle of swim shall be sin (y) =800/1000=0.8

So angle of swim y is 53.13 degrees