No, when a projectile is launched horizontally, its velocity does not increase uniformly throughout the flight. In fact, the velocity remains constant in the horizontal direction throughout the entire trajectory. This is because there are no horizontal forces acting on the projectile once it is launched, assuming no air resistance.
When a projectile is launched horizontally, it has an initial horizontal velocity component but no initial vertical velocity component. The only force acting on it is the vertical force due to gravity. As a result, the projectile follows a curved path known as a parabola.
While the horizontal velocity remains constant, the vertical velocity changes due to the acceleration caused by gravity. The vertical velocity increases downward as the projectile moves downward and decreases upward as it moves upward. At the highest point of the trajectory (the apex), the vertical velocity becomes zero before it starts to decrease in the opposite direction.
Although the magnitude of the velocity changes during the projectile's flight, the change occurs only in the vertical direction. The horizontal velocity component remains constant because there are no forces acting on it in that direction.