Question

A bomb of mass $3kg$ is kept inside a closed box of mass $3kg$ and length $4L$ at its center. It explodes in two parts of mass $m$ and $2m$. The two parts move in opposite direction and stick to the opposite side of the wall of the box. A box is kept on a smooth horizontal surface. What is the distance moved by the box during this time interval?

Answer 1

Since, the bomb is exploding due to internal forces and there is no external force acting either on bomb or box.

i.e.,

$F_{ext}=0$

From Newton's II law,

$F_{ext}=$mass$\times$acceleration

i.e., $F_{ext}=Ma$

$\Rightarrow M_a=0$

$\Rightarrow a=0$.