Which object is in static equilibrium?

a rolling ball that has a net force acting on it
a cruising car that has no net force acting on it
a book that has no net force acting on it and is sitting on a table
a vase that has a net force acting on it and is sitting on a shelf

Aplayground merry-go-round has a radius of 4.6 m and a moment of inertia of 200 kg-m2 and turns with negligible friction about a vertical axle through its center. a child applies a 26.0 n force tangentially to the edge of the merry-go-round for 15.0 seconds. if the merry-go-round is initially at rest, how much work did the child do on the merry-go-round?