Correct Answer to Question 12

As the ball approaches the top of its trajectory, its velocity gets smaller and smaller. The highest point is when the velocity is zero. Therefore it is instantaneously at rest at the top.

However, it is notin equilibrium. The force of gravity is pulling downward on it, while there are no upward forces. The net force acting on the ball is not zero, so it cannot be in equilibrium.

How can it be at rest but not in equilibrium? Because it is only instantaneouslyat rest; it does not remain at rest. If it were in equilibrium, it would remain at rest.

Correct answer: A

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