Question

A boy swims in a straight line to reach the other side of a river. His velocity is 5 ms–1 and the angle of swim with shore is 30°. Flow of river opposes his movement at 2 ms–1. If width of river is 200 m, where does he reach the other bank?
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Answer 1

Velocity of river

Vr = −2i^

Velocity of swimmer w.r.t river is

Vs = 5cos30 i^ + 5sin30 j^

= 4.33 i^ + 2.5 i^

Using

VR = Vs + Vr, we get

VR = 2.33 i^ + 2.5 j^

Time taken by the swimmer=

(Distance Along Y axis) / (Y component of Velocity)

= 200/ 2.5

= 80s

Distance moved along x-axis,

O′F= X component of relative velocity × time.

= 2.33×80

= 186.4m

so, he reach the other bank 186.4 m upstream (ans.)