Question

If action is always equal to reaction explain how a cart pulled by a horse can be moved?

Answer 1

the horse pushes the ground with its foot in the backward direction by pressing the ground. as a result of this force of action(i e backward push) the ground pushes the horse in the forward direction hence the horse pulls the horse.

Answer 2

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When the horse walks in the forward direction (with the cart attached to it), it exerts a force in the backward direction on the Earth. An equal force in the opposite direction (forward direction) is applied on the horse by the Earth. This force moves the horse and the cart forward.

The velocity at which the horse can move by applying a force on the earth depends on the mass of the horse (and the cart attached to it). The heavier the cart, the slower the motion of the horse (for a given amount of force applied by the horse on the Earth). If the cart is too heavy, the force exerted by the horse on the Earth will be insufficient to even overcome the force of inertia. In this case, the horse will not be able to pull the cart.