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NEET 2019 · Relative Velocity in Two Dimensions

Relative Velocity in Two Dimensions question from NEET 2019

Q18NEET 2019Easy

Relative Velocity in Two Dimensions

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:

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Answer: (d)

  1. For the shortest path the resultant must point due north, so he heads upstream (west of north).
  2. sin⁡θ=vrvs=1020=12⇒θ=30∘\sin\theta = \frac{v_r}{v_s} = \frac{10}{20} = \frac{1}{2} \Rightarrow \theta = 30^\circ
  3. So the answer is (d) 30∘30^\circ west of north.
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