Why does this work?? (X and Y independent) There is an image attached to refer to my question. A ballistics cart traveling at constant velocity can shoot a projectile straight into the air and the projectile will be caught in the car when it lands because of the independence of the X and Y components. In the image attached, because the cart is rolling down an incline it does not maintain a constant velocity. However, the ball is still caught. I don't understand why???? The projectile is maintaining the same horizontal velocity while it is in the air, but isn't the horizontal velocity of the cart - parallel to the ground, not parallel to the plane - increasing? After all, the cart is accelerating down the plane, so isn't it getting faster in the y-direction (perpendicular to the ground) and the x-direction (parallel to the ground)???? It just seems as though the projectile should fall behind the cart???