Question

A man can swim 2km/h in still water. Find at what angle to the bank he must head if he wishes to swim directly across a river flowing at a speed of 1km/h.

I don't understand how to find that.

Answer 1

call x across the river
y up river
then y component must come out = 0
that means 2 sin T -1 = 0
sin T = 1/2
T = 30 degrees from x axis toward upstream.