A `400 m` wide river is flowing at a rate of `2.0 m s^-1`. A boat is sailing with a velocity of `10 m s^-1` with respect to the water, in a direction perpendicular to the river.
(a) Find the time taken by the boat to reach the opposite bank.
(b) How far from the point directly opposite to the starting point does the boat reach the opposite bank ?
( c) In what direction does the boat actually move ?

Options

A. 40sec, 80m
B. 30sec,40m
C. 20sec,20m
D. 35sec,80m

Answer

a

Explanation

As it is given that boat is salling 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 `(400)/(10)=40`s.
Drift due to flow of river=Drift velocity xxTime to cross the river
Here boat is sailing in normal direction so direction of drift velocity is the river current velocity. Thus, dirft x=2.0xx40=80m.