A ring of mass `m_(1)` and radius R is fixed in space at some location. An external agent brings a point mass `m_(2)` from infinity to centre of the ring. Work done by the external agent will be

Options

A. `-(Gm_(1)m_(2))/(R)`
B. `(Gm_(1)m_(2))/(R)`
C. `(Gsqrt(m_(1)^(2)+m_(2)^(2)))/(R)`
D. `(Gm_(1)m_(2))/(R(m_(1)^(2)+m_(2)^(2)))`

Answer

A

Explanation

Work done, `W=DeltaU=U_(f)-U_(i)=U_(f)("as " U_(i)=0)`
`rArr W = -(Gm_(1)m_(2)//R)`.