Question

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

• A. 3 $m{s}^{-1}$
• B. 5 $m{s}^{-1}$
• C. 7 $m{s}^{-1}$
• D. 2 $m{s}^{-1}$

Answer 1

Answer: (B)

5 $m{s}^{-1}$

Here,

Velocity of water flowing in river, $v_r=3m{s}^{-1}$

Velocity of swimmer in still water, $v_s=4m{s}^{-1}$

From figure,

The resultant velocity of the swimmer is

$v=\sqrt{v_s^2+v_r^2}=\sqrt{(4{)}^2+(3{)}^2}=\sqrt{25}=5m{s}^{-1}$