Which example best demonstrates how unbalanced forces change the speed of an object's motion? a) a child on a bicycle braking at a stop sign. b) a child singing a song. c) a child sitting in a chair reading a book. d) a child walking around the corner of a school hallway.

A) A child on a bicycle braking at a stop sign.

Explanation:

The child is applying the brakes to dramatically slow down the movement of his body, which couldn't be done without the bike. The bike is acting the same as a car would to us, it propels us and is capable of slowing down or stopping our motion whenever we need.

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