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A boat crosses a river with a velocity of $8 km/h$. If the resulting velocity of boat is $10 km/h$ then the velocity of river water is
Explanation
$\vec{v}_{br} = \vec{v}_{b} + \vec{v}_{r}$ $\Rightarrow v_{br} = \sqrt{v_{b}^{2} + v_{r}^{2}}$ $\Rightarrow 10 = \sqrt{8^{2} + v_{r}^{2}}$ $\Rightarrow v_{r} = 6 km/hr$