Question

according to newtons third law why a cart moves when a horse pulls it?

Answer 1

the third law talks of action and reaction. the horse and cart exert and equal and opposite reaction upon each other.

you need to look at the first law to understand whether the cart will actually move.

if it is going to change speed or direction (acceleration), you will find in the second law the rate at which the rate of motion of the cart will change (though, in the common expression, the rate of change is usually expressed as a constant).

Answer 2

the third law effect is the cart and the horse stick together and sigma F for this system is yeah, the force from the horse (to the floor of course)

Answer 3

both of them are in one system moving in one direction. so horse pulls it with more force than the amount of reaction force exerted by the cart.

Answer 4

The ground where the horse steps give it a reaction force which assist it in moving forward.