Question

A person weighing 60 kg in a small boat of mass 140 kg that is at rest, throws a 5 kg stone in the horizontal direction with a velocity of $14m{s}^{-1}$ . The magnitude of velocity of the boat immediately after the throw is:

• A. $1.2m{s}^{-1}$
• B. $0.5m{s}^{-1}$
• C. $0.35m{s}^{-1}$
• D. $0.65m{s}^{-1}$

Answer 1

Answer: (C)

$0.35m{s}^{-1}$

As there is no external force applied, momentum of system will remain conserved.
Initial momentum $=$ final momentum
$\Rightarrow$ $\left(5\right)\left(14\right)=(140+60)\left(V\right)$, finally system (boat + person) will move with velocity $V$.
This gives $V=0.35m/s.$