Question

A man wants to cross the river of width d in minimum time. Find the taken to cross the river if speed of water flow is u and speed of man with respect to water is v.

Answer 1

Explanation:

Minimum time is when the man moves perpendicular to flow of river. If he has to reach point P then his velocity perpendicular to the flow of river is √v^2−u^2

, so he can reach in time d√v^2 −u^2.

If the river velocity is more than the relative velocity of man then his velocity can never be zero in the direction of flow and thus, he cannot reach point P.