in details?

Question

A swimmer is capable of swimming 0.30 m/s in still water.
(a) If she aims her body directly across a 75 m-wide river whose current is 0.60 m/s, how far downstream (from a point opposite her starting point) will she land?
m
(b) How long will it take her to reach the other side?
s

Answer 1

I'll solve (b) first. If she swims directly across, the downstream component of motion doesn't matter. She swims across at 0.30 m/s and the river is 75 m wide, so it takes her (75 m) / (0.30 m/s) = 250 s.

a) During the 250 s she spends swimming, the current carries her downstream a distance of (250 s)(0.60 m/s) = 150 m.