Final answer:
The net force on the wagon is calculated by subtracting the friction force from Bree's pulling force, resulting in 13 N to the right.
Step-by-step explanation:
The question asks us to find the net force acting on a wagon. Bree pulls the wagon with a force of 18 N to the right, and there is a friction force of 5 N to the left. In addition, the wagon has a weight of 30 N, and the road exerts an upward force of 30 N. Because the forces in the vertical direction (the weight and the upward force from the road) are equal and opposite, they cancel each other out. Thus, they do not affect the horizontal motion of the wagon. To calculate the net force, we take the difference between the force applied by Bree and the friction force:
Net force = Force applied by Bree - Friction force
= 18 N - 5 N
= 13 N to the right.
Therefore, the correct answer is (a) 13 N to the right.