Question

A body $A$ of mass $M$ while falling verticallly downwards under gravity breaks into two parts: a body $B$ of mass $\frac{M}{3}$ and a body $C$ of mass $\frac{2M}{3}$. The centre of mass of bodies $B\&C$ taken together shifts compared to that of body $A$ towards

• A. depends on height of breaking
• B. does not shift
• C. body $C$
• D. body $B$

Answer 1

The correct option is B does not shift

The forces responsible for the breaking of the body into two parts are internal forces, and in horizontal direction,
$F_{\text{ext}}=0$ on the mass $M$.
Or, $\Delta x_{\text{CM}}=0$

$Mg$ being the only external force acting on the system both before and after the breaking, acting in vertically downwards direction.

$\therefore \text{COM}$ will continue moving vertically downward with acceleration $g$ and there will not be relative shift of the $\text{COM}$ of system towards either $B$ or $C$.