Final answer:
When a man pulls an empty wagon causing it to accelerate, it means that there is a net force acting on the wagon. This net force is provided by the man's pull and is directed in the same direction as the pull. The correct answer is option C
Step-by-step explanation:
If a man pulling an empty wagon causes it to accelerate at 1.4 m/s², the most likely scenario is on a flat surface. When the wagon moves uphill or downhill, the gravitational force comes into play, influencing the acceleration. Uphill motion typically results in a decrease in acceleration due to the opposing gravitational force, while downhill motion may lead to an increase in acceleration. However, the provided information doesn't specify the direction of the acceleration. On a flat surface, the applied force by the man overcomes friction and allows the wagon to accelerate.
The scenario of the wagon being on a curved path (Option D) could also contribute to acceleration, but this would involve additional forces such as centripetal force related to circular motion. Without further details, the most reasonable assumption is that the acceleration occurs on a flat surface (Option C), where the applied force can most directly influence the wagon's motion.