A zero instantaneous velocity does not remove the gravitational acceleration. With up chosen positive, a is negative during both upward and downward motion. This is ordinary constant-acceleration kinematics.

The model has a domain of validity. Explain its assumptions before using it in a changed context, then compare your prediction with evidence.

• Ignoring air resistance near Earth, gravity accelerates motion downward at about 9.8 m/s², even at the top of a throw.
• The top is a momentary stop, not a moment without gravity.