You are riding in a boat whose speed relative to the water is 6.9 m/s. The boat points at an angle of 25.0° upstream on a river flowing at 15.1 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 26.5 m wide.

Answer 1

It does not matter how fast the water is flowing. That just affects where on the opposite side you wind up.

Since the boat is moving at an angle of 25.0° upstream, the distance traveled is given by

26.5/d = cos 25.0°

divide the distance by the speed to get the travel time:

t = d/s = (26.5/cos25.0°)/6.9 = 4.23 s

Q: what the heck puny river is only 26.5m wide? That's barely a crick!