When a particle is located a distance $ x $ meters from the origin, a force of $ \cos (\frac{\pi x}{3}) $ newtons acts on it. How much work is done in moving the particle from $ x = 1 $ to $ x = 2 $? Interpret your answer by considering the work done from $ x = 1 $ to $ x = 1.5 $ and from $ x = 1.5 $ to $ x = 2 $.