Question

A boat is sent across (perpendicularly) w.r.t. to the river flow with a velocity of $12km{h}^{-1}$. If the resultant velocity of the boat is $13km{h}^{-1}$, the river is flowing with a velocity of

• A. $12km{h}^{-1}$
• B. $13km{h}^{-1}$
• C. $5km{h}^{-1}$
• D. None of the above

Answer 1

The correct option is C $5km{h}^{-1}$

Let the velocity of the river be $v$.

From the figure,

${12}^2+v^2={13}^2$(using Pythagoras theorem)
$\Rightarrow v=5km/h$