The Horse-Cart Problem and Newton’s Third Law.
I. The horse pulls the cart, and the cart pulls the horse with an equal and opposite force.
II. The system moves because the force exerted by the horse on the cart is greater than the force exerted by the cart on the horse.
III. The horse is able to move forward because the ground pushes the horse forward (reaction force) in response to the horse pushing the ground backward.
IV. The cart moves because the pull of the horse exceeds the frictional force acting on the cart wheels.
V. The tension in the rope connecting the horse and cart is an internal force for the combined Horse-Cart system.
