The net force on a car is zero in both the horizontal and vertical directions. Which two situations could be true about the motion of the car? The car is speeding up onto the highway. The car is parked. The car is moving at a fixed speed and direction. The car is braking (slowing down). The car is being struck by another car.

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.