Three identical spheres , each of mass 3 kg are placed touching each other with their centres lying on a straight line . The centres of the sphere are marked atP ,Q and R respectively .The distance of centre of mass of system from P is

Options

A. `(PQ+QR+PR)/(3)`
B. `(PQ+PR)/(3)`
C. `(PQ+QR+PR)/(9)`
D. `(PQ+PR)/(9)`

Answer

B

Explanation

`X_(CM)=(3xx0+3xxPQ+3xxPR)/(3+3+3)`
`=(3(PQ+PR))/(9)`
`=(PQ+PR)/(3)`