(20 pts) a particle of mass where k is positive constant. a) calculate the effective potential energy, vefs). b) for what t radius, ro, about the force center. c) calculate the angular frequency of this circular orbit. d) calculate the frequency of small radial oscillations, that is, the frequency of motion when the particle is slightly disturbed from a circular orbit. note: the equations of motion in two dimensional polar coordinates are m moves in an attractive central force, f =-郜(ie, v-k), otal energy, e, and angular momentum, l, will the orbit be a circle of