The body is thrown at an angle to the horizon. At what point of the trajectory is the body’s velocity perpendicular

The body is thrown at an angle to the horizon. At what point of the trajectory is the body’s velocity perpendicular to the force acting on the body? Consider air resistance to be negligible. Justify your answer.

At the top of the trajectory. At this point, the vertical component of the velocity is zero. Because the force of air resistance can be neglected, then the horizontal component of the velocity does not change and at the top point of the trajectory the body’s velocity will be directed horizontally. The force of gravity at any point on the trajectory is directed vertically downward.