Question

A boat crosses a river with a velocity of $8km/h$. If the resulting velocity of boat is $10km/h$ then the velocity of river water is

• A. $8km/h$
• B. $6km/h$
• C. $4km/h$
• D. $10km/h$

Answer 1

The correct option is B $6km/h$

Step 1:
Draw a labelled diagram.

Step 2:
Find the velocity of river water.
Given,
$v_B=8km/h$
$v_{br}=10km/h$

${\overrightarrow{v}}_{br}={\overrightarrow{v}}_b+{\overrightarrow{v}}_r$

${\overrightarrow{v}}_{br}=\sqrt{v_b^2+v_r^2}$

$\Rightarrow 10=\sqrt{8^2+v_r^2}$

$\Rightarrow v_r=6km/hr$

Final Answer: (b)