Final answer:
The child on a playground merry-go-round must exert an inward force to maintain his circular motion, which is known as the centripetal force, thus the answer is (a) Inward.
Step-by-step explanation:
A 19kg child is riding a playground merry-go-round and is experiencing a centripetal force. When an object, such as a child on a merry-go-round, moves in a circular path, it must experience a force that points towards the center of the circle in order to maintain its circular motion; this force is known as the centripetal force.
To stay on the merry-go-round without flying off, the child must exert an inward force toward the center. As a result, the correct answer is (a) Inward. The child's force does not exert outward, upward, nor downward in the context of maintaining circular motion on the merry-go-round.
The concept of centripetal force is important in understanding circular motion in physics. It is the force that keeps an object moving in a circle and is always directed towards the center of the object's circular path.
We can use examples from the references provided, where a 22.0-kg child needs to exert a specific centripetal force to stay on a rotating merry-go-round at different speeds and distances from the center, to illustrate why the direction of the force must be inward.