Question

A river $400m$ wide is flowing at a rate of $2.0m/s$. A boat is sailing at a velocity of $10.0m/s$ with respect to the water, in a direction perpendicular to the river. How far from the point directly opposite to the starting point does the boat reach the opposite bank?

• A. $0m$
• B. $40m$
• C. $40\sqrt{3}m$
• D. $80m$

Answer 1

The correct option is D $80m$


Here $\theta$ is zero
As it is given that boat is sailing in a direction normal to current.
Crossing velocity of boat is $=10m/s$
So time taken by the boat to reach the other bank is $=\frac{400}{10}=40s$
Drift due to flow of river is $=$ Drift velocity$\times$time to cross the river

Here boat is sailing in normal direction so drift velocity is the river current velocity.
Thus, drift is
$x=2\times 40=80m$