Question

please solve this question ..........please......​

Answer 1

In this case, the velocity of boat is less than the river flow velocity. Hence, boat cannot reach the point directly opposite to its starting point, i.e., drift can never be zero.

Suppose the boat starts at an angle θ from the normal diraction up stream

Component of the velocity of boat along the river,

vx=u−vsinθ

and velocity perpendicular to the river, vy=vcosθ

time taken to cross the river is t=dvy=dvcosθ

Drift x=(vx)t=(u−vsinθ)dvcosθ=udvsecθ−dtanθ

The drift x is minimum when dxdθ=0

or (udv)(secθ.tanθ)−dsec2θ=0

or uvsinθ=1⇒sinθ=vu

i.,e., for minimum drift, the boat must move at an angle θ=sin−1θ

=sin−1(vu)=sin−1(1)n from the normal direction.