If action is always equal to reaction, explain why a cart pulled by a horse can be moved.

Asked by  | 23rd Apr, 2009, 05:56: PM

Expert Answer:

Following forces are acting on the system of horse and cart:

( i) The weight of the horse and the cart acting vertically downward.

(ii) The reaction of the ground due to horse and cart acting vertically upward.

(iii) The force exerted by the horse with its feet on the ground in backward direction.

(iv) The reaction of the ground on the feet of the horse in the forward direction.

(v) The force of friction acting on the cart in the backward direction.

As far as forces (i) and (ii) are concerned , they are equal and opposite balanced forces so, they cannot produce any motion. Force (iii) is too small to push the earth backward. However, force (iv) i.e. , the reaction of the ground is large enough to push the horse and the cart attached to it in the forward direction as this force is larger than the force of friction due to ground. Thus it is the pair of unbalanced forces (iv) and (v) which make the system of horse and cart move in the forward direction.

Answered by  | 23rd Apr, 2009, 11:09: PM

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