# College Physics

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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

• College Physics -

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

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