A horse is attached to a cart that is at rest behind it. Which force, or combination of forces, explains how the horse-cart system can accelerate from rest?
a. The forward static friction force of the ground on the horse is greater than any friction forces acting backward on the cart, providing a forward acceleration.
b. The forward force of the horse on the cart is greater than the backward force of the cart on the horse, providing a forward acceleration.
c. The force of the horse’s muscles on the rest of the horse-cart system provides the necessary acceleration.
d. The upward normal force of the ground on the horse is greater than the horse’s weight, providing an upward acceleration