What is a useful application for this new material?

Which explanation describes the forces involved for a person to walk down the sidewalk? a. the person's feet push backward on the sidewalk; the sidewalk pushes backward on the person. b. the person's feet push forward on the sidewalk; the sidewalk does not push on the person. c. the person's feet push backward on the sidewalk; the sidewalk pushes forward on the person. d. the person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.

If jerome is swinging on a rope and transferring energy from gravitational potential energy to kinetic energy, is being done.

Does anyone have the answers to online physics course plato course physics, semester a v3.0