A river of width 400 m flows with speed 3 m/s. A swimmer can swim with speed 5 m/s relative to still water. In what direction relative to the river flow should the swimmer head to cross the river in the minimum possible time, and what is that minimum time?

Answer and explanation

Correct answer: A. Perpendicular to river flow (90°); time is 80 seconds

  1. Step 1: To cross in minimum time, the component of swimmer velocity perpendicular to the river bank must be maximized.
  2. Step 2: Swimmer should point directly across the river (perpendicular to river flow, angle 90°).
  3. Step 3: Crossing speed = v_swimmer = 5 m/s.
  4. Step 4: Minimum time = width / v_swimmer = 400 / 5 = 80 seconds.

Practise more Kinematics.

Free questions with an explanation for every one, and full timed JEE Advanced mock tests.

All Kinematics questionsTake a mock test

More Kinematics questions