Question

A boat of mass $40\, kg$ is at rest. A dog of mass $4 \,kg$ moves in the boat with a velocity of $10\, m/s$. What is the velocity of boat?

• A. 4 m/s
• B. 2 m/s
• C. 8 m/s
• D. 1 m/s

Answer 1

Answer: (D)

1 m/s

Answer 2

Total momentum of boat $+$ dog system is conserved. From law of conservation of linear momentum, momentum of boat $=$ momentum of dog $m_{1} v_{2}=m_{2} v_{2}$ $m_1 = 40\,kg$ Given, $v_{1}=?, m_{2}=4\, kg , v_{2}=10 \,m / s$ $\therefore 40 \times v_{1}=4 \times 10$ $\Rightarrow v_{1}=\frac{4 \times 10}{40}=1\, m / s$