Question

If action is always equal to the reaction, explain how a horse can pull a cart?

Answer 1

When the horse exerts a force on the cart,the cart gets subjected to four forcesin all i.e the gravitational force,normal reaction offered by the ground,the external force exerted by the horse on the cart and the frictional force offered by the ground.the first two forces balance each other and hence play no role in motion of the cart.However,the external force exerted by by the horse is partly balanced by the frictional force but the remaining unbalance force causes motion of the cart.

Answer 2

Answer:

According to the Newton's third law of motion, the house exerts some force on the card, and the cart exerts an equal and opposite force on the horse. So, at first glance it seems that the action and reaction forces being equal and hence the cart would not move. But it should be noted that it is only the force on the cart which determines whether the card will move or not, and that the force exerted by the cart on the horse affects the horse alone. Thus, if the horse is able to apply a force to overcome the frictional force present, the cart will move. So, to make the cart move the horse bends forward and pushes the ground with its feet. When the forward reaction to the backward push of the horse is greater than the opposing frictional forces of the waves, the cart moves.