Two particles $A$ and $B$ initially at rest, move towards each other under mutual force of attraction. At an…
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 $3 v$, the speed of centre of mass is
$v$
$4 v$
$2 v$
Zero
Solution
Only internal force is acting on the system. Therefore $\vec{F}_{\text {ext }}=0$. It is also given that the initial velocity of COM is zero, therefore it will remain at rest.