Question

explain very briefly why a horse cannot pull a cart and run in empty space

Answer 1

A horse doens't have much power as a bull.

Answer 2

When a horse is trying to pull a cart,he the ground backwards at an angle from the horizontal.The ground also apply equal reaction force on the feet of the horse in opposite direction.The vertical component of reaction balances the weight of the horse and horizontal is responsible for motion of the cart.In empty spaces,there is no reaction force,therefore a horse cannot pull a cart.