The mass density of a spherical galaxy varies as k/r over a large distance r from its center. ​

Question

The mass density of a spherical galaxy varies as \(k \over r\) over a large distance r from its center. In that region, a small star is in a circular orbit of radius R. Then the period of revolution, T depends on R as:

Answer 1

for circular motion gravitational force will provide required centripital force or