First slide

Motion in a plane

Question

The speed of a swimmer in still water is 20 m/s. The speed of river water is 10 m/s and is flowing due east. If he is standing on the south bank and wishes to cross the river along the shortest path, the angle at which he should make his strokes w.r.t. north is, given by

Moderate

Solution

$cosϕ = \frac{10}{20} = \frac{1}{2} or ϕ = 60 °$
$\Rightarrow θ = 180 ° - (90 ° + 60 °) = 30 °$

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