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To me, the horse's role is merely to transmit the force it is being pushed forward with by the ground over to the cart. So, let's say, the ground pushes horse with 20 N, the horse pulls cart with 20 N, the cart pulls horse with 20 N. If the force that the ground pushes the horse with is doubled, the force on the horse by the cart and on the cart by the horse should also be doubled and we are still left with 0 net force.


marked as duplicate by ACuriousMind, user36790, sammy gerbil, heather, user259412 Aug 27 '16 at 5:50

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  • $\begingroup$ If you look at the forces on the cart, it only has 20N pulling it in the forward direction (The horse pulling the cart), thus it will accelerate. $\endgroup$ – Cort Ammon Aug 26 '16 at 0:54
  • $\begingroup$ Also worth noting is that if the horse and cart are accelerating, they are coupled so they must accelerate at the same rate. In this case, the horse will not actually apply 20N to the cart, it will apply less force than that, and the remaining (unbalanced) force will go into accelerating itself forward. The exact distribution of force will depend on the masses of the horse and cart. $\endgroup$ – Cort Ammon Aug 26 '16 at 0:58

If the horse pushes the ground with a force of 20 N, then the ground also pushes the horse. Hence, the horse would have a forward motion. In addition, if you draw the Free Body Diagram of the cart, you will find that the net force acting on the cart is in the forward direction.

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  • $\begingroup$ Could you tell how horse is able to pull the cart?is the incident like this,the horse pulls the cart forward with some muscular force and then a force equal in magnitude is applied on the horse in opposite direction,but the horse then push the ground backward with a greater force and thus prevents itself from getting pulled backward.am i right? $\endgroup$ – Navneet Kumar Aug 26 '16 at 10:49
  • $\begingroup$ (I'm guessing you are a JEE aspirant, like me). I think you are on the right track. The trick to understanding this concept is to know that Newton's Third law acts on different objects. A more detailed explanation here: lhup.edu/~dsimanek/physics/horsecart.htm $\endgroup$ – Zwolf Aug 26 '16 at 15:18

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