A particle of mass m is under the influence of the gravitational field of a body of mass M (≫ m). The particle is moving in a circular orbit of radius r₀ with time period T₀ around the mass M. Then, the particle is subjected to an additional central force, corresponding to the potential energy Vc(r) = mα/r³, where α is a positive constant of suitable dimensions and r is the distance from the center of the orbit. If the particle moves in the same circular orbit of radius r₀ in the combined gravitational potential due to M and Vc(r), but with a new time period T₁, then (T₁² − T₀²)/T₁² is given by [G is the gravitational constant.]