"A particle of mass m is constrained to move without friction on the inner surface of a revolution paraboloid under the action of gravity. The equation of this revolution paraboloid is x^(2) + y^(2) = az, where a is a constant (gravity acts in the direction of negative z).
a) Write the Lagrangian of the system using cylindrical coordinates ρ and φ as generalized coordinates, which will involve a cyclic coordinate. Then obtain the equations of motion, one of which should be homogeneous (i.e., involving only one coordinate).
b) Show that there exists a solution where the particle moves at z > 0 constant and find the values of ρ and φ ˙ for this solution. Consider a small perturbation from this stable motion (ρ = ρ0 + η(t) and φ ˙ = φ0 ˙ + ω(t) where η << 1 and ω << 1), and solve completely for the particle's motion in this regime. What does this motion consist of?"