Question

A swimmer wishes to cross a 500 m wide river flowing at 5 km/h. His speed with respect to water is 3 km/h.
(a) If he heads in a direction making an angle θ with the flow, find the time he takes to cross the river.
(b) Find the shortest possible time to cross the river.

Answer 1

b) Here vertical component of velocity i.e. 3 km/hr takes him to opposite side.
Time =Distance/Velocity = 0.5/3 = 0.16 hours
Distance=0.16 hr = 60 × 0.16 = 9.6 = 10 minute.