Find the distance between centre of gravity and centre of mass of a two particle system attached to the ends of a light rod. Each particle has same mass. Length of the rod is R, where R is the radius of earth.

Options

A. (a) R
B. (b) R/2
C. (c) zero
D. (d) R/4

Answer

B

Explanation

Centre of gravity of the two particles
`X_(CG)=(W_(1)X_(1)+W_(2)X_(2))/(W_(1)+W_(2))=((0)(0)+(mg)(R))/(0+mg)=R`
the centre of mass of the two particle system is at
`X_(CM)=(M(R)+m(0))/(2M)=(R)/(2)`