(a) Since the locomotive and truck are moving at a constant speed, the net force is zero. Therefore, the tension in the coupling is 0 N.

(b) The power produced by the locomotive's engine is given by the formula \(P = Fv\), where \(F\) is the force and \(v\) is the velocity. The resistance force is 0.2 N, and the velocity is 2 m/s. Thus, \(P = 0.2 \times 2 = 0.4 \text{ W}\).

(c) When the power is changed to 1.2 W, the driving force \(DF\) is \(\frac{1.2}{2} = 0.6 \text{ N}\). Using Newton's second law for the locomotive: \(DF - 0.2 - T = 0.8a\). For the truck: \(T = 0.4a\). For the system: \(DF - 0.2 = 1.2a\). Solving these equations gives \(T = \frac{2}{15} \text{ N}\).