College Physics
posted by DumbDumb on .
A hunter wishes to cross a river that is 1.6 km wide and flows with a speed of 5.0 km/h parallel to its banks. The hunter uses a small powerboat that moves at a maximum speed of 15 km/h with respect to the water. What is the minimum time necessary for crossing?
min

depends on whether he cares how far downstream the boat drifts. Minimum time is achieved by heading perpendicular to the bank. In that case, he has to go 1.6km at a speed of 15km/hr.
min time is thus 1.6km / 15 km/hr = .10666 hr = 6.4min