Question

if action is always equal to the reaction. explain how a horse can pull a cart.

Answer 1

Hello! I can help you :)
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Newton's third law of motion:

Every action has an equal and opposite reaction.

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A horse applies it's force on the ground. Here, the horse pushes the ground backwards in order to move forward. According to Newton's third law, an action must have an equal reaction, thus the ground exerts force which pushes the horse forward (The opposite direction). The reaction force is exerted by the earth which helps the horse move forward. As the cart is attached to the horse, as a result it moves forward along with the horse.
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Answer 2

Heya friend,

According to Newton's Third law of motion action is always equal to the reaction in opposite direction.

Horse can pull a cart, when the horse starts pushing the the ground backwards from his feet, then ground also produces equal reaction forward on the feet of the horse. And then cart moves forward.

Hope it helps...!!