Explanation:

The correct answer to the given question is option C, which states that the boy is in accelerated motion. Let's understand why this is the correct answer.

Motion of the Boy:

The boy is enjoying a ride on a merry-go-round, which means he is spinning in a circular path. The merry-go-round is moving with a constant speed of 10 m/s.

Uniform Circular Motion:

When an object moves in a circular path with a constant speed, it is said to be in uniform circular motion. In this case, the merry-go-round is moving with a constant speed, so it is in uniform circular motion.

Acceleration in Uniform Circular Motion:

Although the speed of the boy on the merry-go-round is constant, he is still considered to be in accelerated motion because his direction of motion is changing continuously. Acceleration is defined as the rate of change of velocity, and velocity includes both speed and direction. In uniform circular motion, the direction of the object is changing, which means there is a change in velocity and hence acceleration.

Centripetal Acceleration:

The acceleration in uniform circular motion is known as centripetal acceleration. It is always directed towards the center of the circle and is perpendicular to the velocity of the object. In this case, the boy's acceleration is directed towards the center of the merry-go-round.

Centripetal Force:

The centripetal acceleration is caused by the centripetal force, which is the net force acting towards the center of the circle. In the case of the merry-go-round, the centripetal force is provided by the friction between the boy and the merry-go-round.

Conclusion:

In conclusion, the boy is in accelerated motion because he is moving in a circular path, and although his speed is constant, his direction is continuously changing. This change in direction results in centripetal acceleration, which is responsible for his accelerated motion. Therefore, option C is the correct answer.