Final answer:
The motion of a stone whirled in a horizontal circle is uniform circular motion, as it travels on a circular path at constant speed with changing direction.
Step-by-step explanation:
Understanding Uniform Circular Motion
When a boy whirls a stone in a horizontal circle, the motion of the stone can be characterized as uniform circular motion. This is because the stone is traveling on a circular path at a constant speed, even though its direction is constantly changing. Since the velocity is constant in magnitude but changing in direction, the stone experiences a centripetal acceleration, which is always directed towards the center of the circle. This kind of motion is distinct from linear motion, random motion, and vertical motion, which all have different characteristics. Linear motion involves a straight-line trajectory, random motion has no predictable pattern, and vertical motion involves movement along a vertical plane.
Thus, the correct answer to the question is 1) Uniform circular motion.