A boy is sitting in a merry-go-round which is moving with a constant speed of 10 m/s. This means that the boy is (A) at rest (B) moving with no acceleration (C) in accelerated motion (D) moving with uniform velocity.

Answer: (C) in accelerated motion

The boy is moving constantly at a speed of 10 m/s and since the direction is the same therefore the boy is moving at an accelerated motion.

The rate at which the velocity changes is called acceleration.
Velocity is a vector quantity, and a change in velocity can be caused by a change in magnitude, direction, or both.
The boy is going at a constant speed, but his velocity is changing, therefore he is in accelerated motion.

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