strobe photographs taken of a disk moving from left to right under different conditions. The time interval between images is constant. Taking the direction to the right to be positive, describe the motion of the disk in each case. For which case is

Which body is in equilibrium? (1) a satellite orbiting earth in a circular orbit (2) a ball falling freely toward the surface of earth (3) a car moving with a constant speed along a straight, level road (4) a projectile at the highest point in its trajectory