Your answer touches on some relevant concepts, but let's clarify the explanation based on Newton's First Law of Motion.
Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by a net external force. When you slide a book across a table, it initially moves due to the force you applied. However, as it moves, several forces come into play that eventually cause it to stop:
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Friction: This is the primary force that opposes the motion of the book. The table's surface exerts a frictional force against the sliding book, which acts in the opposite direction of its motion, gradually slowing it down until it stops.
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Gravity: While gravity is acting on the book (pulling it downward), it is not directly responsible for stopping the motion in this case. Instead, it contributes to the normal force between the book and the table, which affects the amount of friction.
In summary, while friction is the main force responsible for the book coming to a stop, gravity plays a supporting role in enabling that friction. So, your answer is not incorrect, but a more precise answer would focus mainly on friction as the force that causes the book to stop, with gravity being a background force.