Physics Problem ||

A point mass m, is constrained to move on the inner surface of a paraboloid of revolution
x^2 + y^2 = az (where a is a positive constant). When it spirals down the surface, under the influence of gravity (along −z direction), the angular speed about the z - axis is proportional to
(a) 1 (independent of z) (b) z (c) z^(-1) (d) z^(-2)