Briefly explain how is a horse able to pull a cart

Explanation

Consider the horse as the system then there are there forces acting on the horse.
(i) Downward gravitational force (m g)
(ii) force exerted by the road (f)
(iii) Backward force exerted by the cart (f )

`F_(r)` force exerted by the road on the horse
`F_(c )` - force exerted by teh cart on the horse.
`F_(e )` II- Parallel component of `F_(r )` which is reason for forward movement.
Let the force exerted by the road can be resolved into parallel and perpendicular components. there is parallel component . so there is net than the backward force along forward dirction which caused the forward movement of the horse.
(i) Downward gravitational force
(ii) Force exerted by the road
(iii) Force exerted by teh horse

The force exerted by teh road `(vec(F )_(r))` can be resoloved into parallel and perpendicualr components . The parallel component acting in the opposible direction hence there is an overall unbalanced force in the forward direction that causes the cart to acceleration forward.
If we take the cart and horse as a system then there are two forces acting on the system they are
(i) Downwards gravitational force
(ii ) the force exerted by the road `(F_(r))` on the system
It is shown in the following figure.
(iii) In this case the force exerted by the road `(F_(r))` on the system is resolved into parallel and perpendicular components . The The perpendicular componenet is the normal force which cancels the downward gravitional fore `(m_(h)+ m_(c ))` g. The parallel component of the force is not balanced hence the system acceleration and moves forward due to this force.