Question

A river is flowing due east with a speed $3\,ms^{-1}$. A swimmer can swim in still water at a speed of $4\,ms^{-1}$. If swimmer starts swimming due north, then the resultant velocity of the swimmer is

• A. $3\,ms^{-1}$
• B. $5\,ms^{-1}$
• C. $7\,ms^{-1}$
• D. $2\,ms^{-1}$

Answer 1

Answer: (B)

Here,
Velocity of water flowing in river, $v_r = 3 \,m s^{-1}$
Velocity of swimmer in still water, $v_s = 4 \,m s^{-1}$
From figure,
The resultant velocity of the swimmer is
$v=\sqrt{v^{2}_{s}+v^{2}_{r}}$
$=\sqrt{\left(4\right)^{2}+\left(3\right)^{2}}$
$=\sqrt{25}$
$=5\,ms^{-1}$