Two particle which are initially at rest move towards each other under the action of their internal attraction. If their speeds are `v` and `2 v` at any instant, then the speed of centre of mass of the system will be

Options

A. `1.5v`
B. v
C. 2v
D. zero

Answer

D

Explanation

`vecV_(cm)=(m_(1)vecv_(1)+m_(2)vecv_(2))/(m_(1)+m_(2))`
Initial velocity of centre of mass
As `vecF_(ext)=0`
`:.DeltavecV_(cm)=0`
`impliesvecV_(cm)=` constant
`:.` Final velocity of centre of mass =0
`:.V_(cm)=0`