Which of these motions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table? Explain your answers.
A falling rock from a cliff is under the effect of gravity and it falls at a constant gravitational acceleration of g=9.8m/s2. So its acceleration is constant.
The elevator moving from second floor to fifth floor must first accelerate from rest to reach a speed. Then it must decelerate to stop at fifth floor. So its acceleration is not constant.
The dish at rest on the table have zero speed and zero acceleration. It has no acceleration.