Question

A boy crosses a river twice
on a straight graph at an
angle - 30" with the
downstream direction,
first time in two minutes
and second time in four
minutes. If his speed
relative to river current is
2. = 3 m/s in both the
attempts, find speed of
the river current.​

Answer 1

River velocity vs.

r =2 I r =2 I r =2 I r =2 I

The swimmer's velocity in relation to the river is v

s =5cos30 I +5sin30 j s =5cos30 I +5sin30 j s =5cos30 I +5sin30

​

=4.33 i ^ +2.5 i ^

Using v

R​= v

s​+ v

r​, we get v

R​=2.33 i ^ +2.5 j ^

​

Time taken by the swimmer= ycomponentofvelocity Distancealongy−axis

​

= 2.5 200​=80s

Distance moved along x-axis, O ′ F=x component of relative velocity × time. =2.33×80=186.4m 186m upstream

Explanation: