Final answer:
Kinematic equations for constant acceleration are not directly applicable to scenarios with non-constant acceleration but can be used over short intervals where acceleration is nearly constant. For variable acceleration, motion may be analyzed in parts with constant acceleration each. Moreover, constant speed with non-zero acceleration is exemplified by uniform circular motion.
Step-by-step explanation:
Kinematic equations derived for constant acceleration cannot be applied to scenarios with non-constant acceleration without some adjustments. While these equations are very useful for studying uniformly accelerated motion, they are not accurate when acceleration varies. However, they can be applied over very short time intervals where acceleration can be considered approximately constant.
For example, a car accelerating to its top speed and then braking to a stop experiences changes in acceleration. To analyze such motion accurately, one must consider the motion in separate parts, with each part having its own constant acceleration.
Regarding constant speed and non-zero acceleration, this is possible in a situation like uniform circular motion, where the speed remains constant but the direction changes, thus resulting in a non-zero acceleration due to the change in velocity's direction.