Question

What is To Cross the River of Width d along the Shortest Path?

Answer

Shortest path is PQ , the boat must move along PR making an angle (90° + θ) with the direction of the stream such that the direction of the resultant velocity v is along PQ (see figure).
Given by, t = d/v = d/√v_b² – v_w²
where, v_w = Speed of stream flow and v_b = Speed of the boat.

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