Question

A boy of mass 40 kg jumps off a boat with a velocity of $3m{s}^{-1}$ . With what momentum does the boat move ?

• A. $-210kg.m{s}^{-1}$
• B. $-120kg.m{s}^{-1}$
• C. $-125kg.m{s}^{-1}$
• D. $-215kg.m{s}^{-1}$

Answer 1

Answer: (B)

$-120kg.m{s}^{-1}$

Using momentum conservation,

$m_1{u}_1+m_2{u}_2=m_1{v}_1+m_2{v}_2$

$m_1=mass$ $of$ $boy$ $m_2=mass$ $of$ $boat$
$m_1=40kg$ $,v_1=3m/s$ $u_1=0$ $u_2=0$

$\Rightarrow 40\times 0+m_2\times 0=40\times 3+m_2\times v_2$

$\Rightarrow 0+0=120+Pboat$

$0=Pboat+120$
$Pboat=-120kgm/s$