Three identical spheres, each of mass 1 kg are kept as shown in figure, touching each other, with their centres on a straight line. If their centres are marked P, Q, R respectively, the distance of centre of mass of the system from P (origin) is

Options

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

Answer

B

Explanation

`x_(CM)= (m_(1) x_(1) + m_(2) x_(2) + m_(3) x_(3))/(m_(1) + m_(2) + m_(3))`
`x_(CM)= (m(0+ PQ + PR))/(3m)`
`x_(CM)= (PQ + PR)/(3)`