For sure - "applications of calculus to the physical world" is a fundamental topic which will get you used to the idea of using calculus to describe an object's motion (kinematics). For example, if you differentiate an object's position with respect to time, you will obtain an expression for velocity, likewise differentiate the velocity to obtain acceleration. Integrating does the opposite - eg integrate acceleration to get velocity.
But are you sure that your teacher is starting 4unit mechanics before covering the 2unit and 3unit "applications" topic? It seems absurd that they would do that because you would end up having to understand the 3unit work first anyway before doing the 4unit problems. If you are just worried because you see mechanics as the next chapter in your text book, don't be, because when I did 4u we didn't follow the order of the textbook so it is likely that you won't either.
Mechanics in 4u pretty much builds on this kinematics with more difficult problems, and also introduces dynamics (describing the forces which cause motion). This part can be a bit difficult especially if you don't do physics, because it is such a different way of looking at things.
By the way, the 4unit mechanics topic is essentially the same stuff you do in first year physics at uni - so if you love it, then perhaps you'd enjoy an engineering or a science degree
However, if you are feeling motivated, by all means get a head start by doing some of the work now but don't get stressed out if you can't. After all, it is only the beginning of the holidays...
Good luck and enjoy your easter break!
