A particle P of mass m slides on the smooth inner surface of a circular cone of semiangle α. The axis of symmetry of the cone is vertical with the vertex O pointing downwards. Take as generalised coordinates r, the distance O P, and φ, the azimuthal angle about the vertical through O.
Obtain Lagrange's equations. Show that φ is a cyclic coordinate and find (and identify) the conserved momentum pφ.