A playground merry-go-round of radius 2.3 m has a moment of inertia 174 kg.m2 and is rotating at 13 rev/min about a frictionless vertical axle. Facing the axle, a 35 kg child hops onto the merry-go-round, and manages to sit down on the edge.
What is the new angular speed of the merry-go-round?
Answer in units of rev/min.