compare and contrast the use D'Alembert's principle with the principle of conservation of energy to solve an engineering problem.
D'Alembert's principle states "The total virtual work of the impressed forces plus the inertial forces vanishes for reversible displacements".
Or as a restatement Newton's Law of Motion F -ma = 0
The law of the conservation of energy states "the total amount of energy in an isolated system remains constant."
So in reality they are statements of the same thing. D'Alembert's Principle is a specialized case that applies to moving objects with out losses due to friction of the general law of conservation of energy.
All real systems are governed by these principles. They is the basis of the proof that perpetual motion is not possible.