A boat is sent across a river with a velocity of $ 8 \mathrm{~km} \mathrm{hr}^{-1} $. If the resultant velocity of the boat is $ 10 \mathrm{~km} \mathrm{hr}^{-1} $, then the velocity of the river is

Question

A boat is sent across a river with a velocity of $ 8 \mathrm{~km} \mathrm{hr}^{-1} $. If the resultant velocity of the boat is $ 10 \mathrm{~km} \mathrm{hr}^{-1} $, then the velocity of the river is, $ 12.8 \mathrm{~km} \mathrm{~h}^{-1} $, $ 6 \mathrm{~km} \mathrm{~h}^{-1} $, $ 8 \mathrm{~km} \mathrm{~h}^{-1} $, $ 10 \mathrm{~km} \mathrm{~h}^{-1} $

MARKS App · Accepted Answer

Let the velocity of the river = v → R ∴ | v → boat | = 8 km h − 1 v → b R = v → b − v → R v → b = v → b R + v → R ∵ v → b R ⊥ v → R v b = v b R 2 + v R 2 v b 2 = v b R 2 + v R 2 ( 10 ) 2 = ( 8 ) 2 + v R 2 v R = 6 k m h - 1

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