Question

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

Total momentum of boat $+$ dog system is conserved.
From law of conservation of linear momentum,
momentum of boat $=$ momentum of dog
$m_1{v}_2=m_2{v}_2$
$m_1=40kg$
Given, $v_1=?,m_2=4kg,v_2=10m/s$
$\therefore 40\times v_1=4\times 10$
$\Rightarrow v_1=\frac{4\times 10}{40}=1m/s$