Final answer:
The cart descending the ramp is subjected to gravity, which is broken down into components parallel and perpendicular to the ramp, the normal force, and friction. The parallel component of gravity accelerates the cart down the ramp, and as it moves, friction acts in opposition.
Step-by-step explanation:
When a student releases a cart from the top of a ramp, the main forces acting on the cart as it moves down the ramp are the force of gravity, the normal force exerted by the ramp on the cart, and the force of friction. The force of gravity can be divided into two components: one acting perpendicular to the ramp which is balanced by the normal force, and the other acting parallel to the ramp's surface, which causes the cart to accelerate downwards. Friction opposes this motion, but if the cart is moving, it indicates that the component of gravity parallel to the ramp surface is stronger than the force of friction.
As the cart descends, its velocity increases due to the unbalanced force acting along the ramp. When the cart eventually leaves the ramp, its velocity relative to the ground is the result of acceleration caused by the net force that has acted on it during its descent.