Notes

To Cross the River in the Shortest Time…

To Cross the River in the Shortest Time, the shortest time is given by, t = d/v_b. At this time, boat will reach point S on the opposite bank of the river at a distance x from Q.
We can write, x = dtanθ = v_w/v_b
⇒ x = d(v_w/v_b) x is also called drift.