Question

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

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

Answer 1

Answer: (B)

6 km/h

Answer 2

$\overset{\rightarrow}{v_{br}} = \overset{\rightarrow}{v_{b}} + \overset{\rightarrow}{v_{r}}$

⇒$v_{br} = \sqrt{v_{b}^{2} + v_{r}^{2}}$

⇒$10 = \sqrt{8^{2} + v_{r}^{2}}$

⇒$v_{r} = 6km ⥂ / ⥂ hr$.