A herdsman yelling out to a fellow herdsman heard his voice reflected by a cliff 4s later. What is the velocity of sound in air if the cliff is 680m away

Asmall 21 kilogram canoe is floating downriver at a speed of 1 m/s. what is the canoe's kinetic energy?

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?

If anyone who can me with this hw? i would really appreciate it