A marble at the front of a truck bed traveling at 20 m/s relative to the highway rolls toward the back of the truck bed with a speed of 7m/s relative to the truck bed. What is the velocity of the marble relative to the highway?

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?