Define gravitational potential energy.

Explanation

Potential energy of a body at a point in a gravitational field is the work done by an external agent in moving the body from infinity to that point.
` vec(E)_("total")= vec(E)_(1)+vec(E)_(2)+vec(E)_(n)= - (Gm_(1))/(r_(1)^(2))hat(r)_(1)-....(Gm_(n))/(r_(n)^(2))hat(r)_(n)`
`vec(E)_("total")=sum_(i=1)^(n) (Gm_(i))/(r_(1)^(2)) hat(r)_(i)`