A river 400 m wide is flowing at a rate of 2.0 m/s. A boat is sailing at a velocity of 10 m/s with respect to the wate, 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?

Answer 1

the downstream problem is perpendicular to and therefore independent of (except in time) the across problem

400 = 10 t
t = 40 seconds

then

d = 2 t = 80 m