A particle moves on the inside surface of a smooth conical shell and is given an initial

Question:

A particle moves on the inside surface of a smooth conical shell and is given an initial velocity v₀ tangent to the horizontal rim of the surface at A. As the particle slides past point B, a distance z below A, its velocity v makes an angle θ with the horizontal tangent to the surface through B. Determine expressions for θ and the speed v.