A river 400 m wide flows at a rate of 2.0 m/s . A boat sails at a...

Let the width of the river be $w = 400 \text{ m}$.

The velocity of the boat with respect to the water is $v_{br} = 10 \text{ m/s}$.

Since the boat is steered perpendicular to the river flow, the time taken to cross the river is given by:

$t = \dfrac{w}{v_{br}} = \dfrac{400}{10} = 40 \text{ s}$

The river flows at a velocity of $v_r = 2.0 \text{ m/s}$.

The drift of the boat, which is the distance from the point directly opposite to the starting point, is calculated as:

$x = v_r \times t$

$x = 2.0 \times 40 = 80 \text{ m}$