D'Alembert's principle help

I am doing an engineering course at college and got some information on what I wanted to learn, I saw a question regarding D'Alembert's priciple and didnt know what it was about, for example it was a question that looked like this: mass x accelerates uniformly from rest to celocity of x in x seconds while ascending a 1 in x gradient, resistence is xKN making use of D'Alberts principle determine the tracktive force between wheels/road, the work done ascending the slops, the average power developed by the enginer.

I am interested in how the principle works and how it would answer this sort of question, does anybody know of any good websites I could use to learn this principle? I tried finding it but end up finding stuff I do not understand, is this a advanced principle?