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Q.
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?
AFMCAFMC 2004Laws of Motion
Solution:
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$
$\therefore 40 \times v_{1}=4 \times 10$
$\Rightarrow v_{1}=\frac{4 \times 10}{40}=1\, m / s$