Question

A man starts at point on a riverbank, tries to swim at an angle of π/3 with riverbank with speed u, reaches a point downstream on the other bank and runs to the point exactly opposite to where he started with speed 2u all in 30 seconds. If river is flowing with a speed u/2, find u in m/s (upto two decimal places)​

Answer 1

The angle made by the person swimming with the direction perpendicular to the flow of water is 120

∘

−90

∘

=30

∘

To reach the point B, drift must be zero, i.e., the relative velocity of boat w.r.t. river, v

br

, should be along perpendicular direction.

Equating the component of velocity along horizontal direction to zero,

v

b

sinθ−v

r

=0

sin30

∘

=

0.5

v

water

or

v

water

=

2

1

×0.5=0.25m/s

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