Question

When a horse pulls a wagon, the force that causes the horse to move forward is the force.

• A. The horse exerts on the wagon
• B. The horse exerts on the ground
• C. The wagon exerts on the horse
• D. The ground exerts on the horse

Answer 1

The correct option is D

The ground exerts on the horse

Consider the free body diagram of the system.

When a horse pulls a cart the following forces are acting on the system

1. The force applied by the horse on the ground.
2. The force is due to the friction between the ground and the cart.
3. The cart will only move if the force applied by the horse is more than the frictional force.

Newton's third law of motion

1. In order to make the cart move, the force must be applied in the direction of the moving cart.
2. But the force applied by the horse on the ground is opposite to the direction of the moving cart.
3. Hence, the force that the horse exerts on the ground, is not the reason for the movement of the cart.
4. On the other hand, according to Newton's third law of motion, the ground will also exert the same amount of force on the horse.
5. The direction of this reaction force by the ground is along the direction of the movement of the cart.

Hence, the reason for the movement of the cart is the force, that the ground exerts on the horse.

Therefore, option (D) is correct.