A ball is falling at terminal velocity. Terminal velocity occurs when the ball is in equilibrium and the forces are balanced. Which free body diagram shows the ball falling at terminal velocity?

At terminal velocity, the ball’s acceleration is zero, so the net force on it must be zero. Choice A shows gravity pulling downward with 20 N and air resistance pushing upward with 20 N; these equal, opposite forces balance. The other diagrams show an unbalanced force.

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