A body of mass 300 g at rest breaks into two parts due to internal forces. One part of mass 200 g is found to move at a velocity of 12 m $s^{-1}$ towards east. Find the velocity of the other part.

The correct option is A 24 m $s^{-1}$ towards west

Mass of one part $m_1=200gm$

Its velocity $v_1=12m/s$ towards east

So, mass of other part $m_2=300-200=100gm$

Let its velocity be $v_2$.

Applying conservation of linear momentum : $P_f-P_i$

Or $m_1{v}_1+m_2{v}_2=0$

Or $200\times 12+100\times v_1=0$

$⟹v_2=-24m/s$

So, the second part will fly off towards west with a velocity of $24m/s$.