A boy of mass 40 kg jumps off a boat with a velocity of 3m/s. With what momentum does the boat move?

A boy of mass 40 kg jumps off a boat with a velocity of 3m/s.The boat move with a momentum of -120kg.m/s.

Using momentum conservation,

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

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

   $v_2= velocity of boat$

   $u_1=0$$u_2=0$

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

$\Rightarrow 0+0=120+P{}_{boat}$ 

here $P_{boat }= momentum of boat$

$0=P{}_{boat}+120$
$P_{boat}= -120 m/s$