Question

Cosider a gravity - free hall in which a tray of mass M , carrying a cubical block of ice of mass m and edge L , is at rest in the middle. If the ice melts, by what distance does the centre of mass of "the tray plus the ice" system descent ?

• A. $\frac{-mL}{2(M+m)}$
• B. $\frac{-mL}{2(M+m)}$
• C. Zero
• D. $\frac{-2mL}{3(M+m)}$

Answer 1

The correct option is C

Zero

$X_{cm}$ = $\frac{m_1{X}_1+m_2{X}_2}{m_1+m_2}$ = 0
But as there is no gravity , the shape of ice even when it melts completely, will remain the same.
Therefore , COM will not move.
This can be concluded that in absemce of net external force on any system its COM does not change its sate with time.