Two particles $A$ and $B$ initially at rest, move towards each other, under mutual force of attraction. At…
Two particles $A$ and $B$ initially at rest, move towards each other, under mutual force of attraction. At an instance when the speed of $A$ is $v$ and speed of $B$ is $2 v$, the speed of centre of mass $(\mathrm{CM})$ is
Zero
$v$
$2.5v$
$4v$
Solution
As initially both the particles were at rest therefore velocity of centre of mass was zero and there is no external force on the system so speed of centre of mass remains constant $i e$, it should be equal to zero.