If I were a passenger in a convertible car traveling at a constant velocity and threw a ball straight up into the air, neglecting air resistance, the ball would follow a parabolic path and would eventually fall back into the car.
When the ball is thrown straight up, it will initially have a vertical velocity of 0 at the top of its trajectory. This means that it will begin to fall back down at the same speed that it was thrown up, due to the force of gravity. Since the car is moving at a constant velocity, the ball will appear to fall back into the car from the perspective of someone inside the car. However, from an outside perspective, the ball will be seen to fall to the ground at a point ahead of the car.
It's important to note that this scenario is based on the assumption that there is no air resistance. In the real world, air resistance would cause the ball to slow down as it moves through the air, which would affect the trajectory of the ball and would likely cause it to fall outside of the car.