PLEASE IM TIMED If total mechanical energy = kinetic energy + potential energy, TME = KE + PE, and a roller coaster has 500 J of total mechanical energy. At the very beginning of the track the roller coaster has 500 J of potential energy, how much kinetic energy is there at the beginning of the track?

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?